Total knee prosthesis with resurfacing and posterior stabilization capability

ABSTRACT

A resurfacing type of total knee prosthesis is disclosed which also provides a posterior stabilization function over the entire range of flexion. The knee prosthesis provides primary or supplementary posterior stabilization of the reconstructed knee joint by means of a unique mechanical cam/follower mechanism, which is integrated within the medial and lateral distal condyles of the femoral component to provide functional compensation for lost, resected or incompetent posterior cruciate ligaments or to work in conjunction with surgically retained viable or questionably viable cruciate ligament structures of the reconstructed knee joint. The invention extends to prostheses including a hinge means that defines a posterior stabilization means separate from that defined by the condyles. One embodiment of the invention extends individually to the posterior stabilizing hinge means.

CROSS-REFERENCE TO RELATED APPLICATION

The present Application is a Continuation-In-Part of application Ser.No. 07/673,790, filed Mar. 22, 1991, by the inventor herein. Priorityunder 35 U.S.C. §120 is claimed as to the above earlier filedApplication, and the disclosure thereof is incorporated herein byreference.

BACKGROUND OF THE INVENTION

The present invention relates generally to knee prostheses and, moreparticularly, to a resurfacing type of total knee prosthesis which alsoprovides a posterior stabilization function over the entire range offlexion, and which in one embodiment includes a hinged construction.

Known total knee prostheses can essentially be classified into threebasic categories. In the first category, the articular surface of thedistal femur and proximal tibia are "resurfaced" with respective metaland plastic condylar-type articular bearing components. These kneeprostheses provide adequate rotational and translational freedom andrequire minimal bone resection to accommodate the components within theboundaries of the available joint space. The patella-femoral joint mayalso be resurfaced by a third prosthetic component, as well. Thefemoral, tibial and patella prosthetic resurfacing components areaffixed to respective, surgically prepared adjacent bone structure by acementing or by a biological bone ingrowth fixation means.

The femoral component is a metallic alloy construction (cobalt-chromealloy or 6Al4V titanium alloy) and provides medial and lateral condylarbearing surfaces of multi-radius design of similar shape and geometry asthe natural distal femur or femoral-side of the knee joint. The tibialcomponent can be made entirely of plastic (UHMWPE: ultra high molecularweight polyethylene) or can be comprised of a metallic base component,distally, and an interlocking plastic (UHMWPE) component, proximally.The plastic tibial plateau bearing surfaces are of concave multi-radiusgeometry to more or less match the articular geometry of the matingfemoral condyles, depending upon the desired design mechanics of primaryfemoro-tibial motion, e.g. the flexion-extension mode-includingposterior rollback and the secondary rotational and translationalarticular motions. In the resurfacing type of total knee prostheses boththe femoral and tibial components are positioned on the respective sideof the knee joint and are not mechanically connected or linked together,as in the case of constrained or hinged type of knee prostheses, whichconstitutes another or second category of total knee prostheses.

Additionally, in resurfacing types of total knee prostheses according tothe first category, as previously stated, the tibial plateau bearingsurface geometry can assume a variety of configurations, depending uponthe desired extent of articular contact congruency and associatedtranslational (medial-lateral and anterior-posterior) and rotational(axial and varus-valgus) secondary femoro-tibial motions. These varioussecondary motions allow the resurfaced knee to function in anatural-like biomechanical manner in conjunction with the surroundingligamentous and muscle structures about the knee joint. The viable softtissue structures functionally maintain the femoral and tibial bearingsurfaces in contact, provide the necessary levels of constraining forceto achieve knee joint stability, and decelerate the principal motion inflexion-extension and secondary motions, such as axial rotation, etc. ina controlled manner. Additionally, this functional interaction betweenthe surrounding tissue structures and the implanted knee prosthesisminimizes abrupt motion stoppage or impact loading of properly designedprosthetic articular surfaces, and thus prevents overstressing at thecomponent fixation interface. Examples of resurfacing types of totalknee prosthetic devices are disclosed in U.S. Pat. Nos. 3,774,244 toWalker; 3,728,742 to Averill et al.; 4,081,866 to Upshaw et al. and4,207,627 to Cloutier.

On the other hand, the mechanically linked, constrained or hinged typeof knee prosthesis according to the second category provides a fixedfulcrum flexion-extension capability. Some of these devices are fullyconstrained in axial rotation, while others provide either partiallyconstrained or unconstrained axial rotational freedom. The "hinged knee"therefore, is usually surgically indicated in selected cases where thesurrounding soft tissue structures are grossly degenerated and incapableof providing functionally acceptable knee joint stability. Examples ofthis type of total knee prosthetic device are disclosed in U.S. Pat.Nos. 3,996,624 to Noiles; 3,837,009 to Walker; and 4,136,405 to Pastricket al.

In clinical situations where prosthetic knee joint reconstruction issurgically indicated in the presence of compromised posterior(tibia-to-femur) stability, that is, due to absent or incompetentposterior cruciate ligament structures, a posterior-stabilized totalknee device can be utilized. This type of device constitutes the thirdcategory of total knee prosthetic devices. The posterior-stabilizedtotal knee device essentially incorporates all of the functionalfeatures of the first category, that is, the resurfacing condylar-typeof knee prostheses, in addition to incorporating a mechanicalcam/follower mechanism for providing posterior (tibia-to-femur)constraint. The cam/follower mechanism is almost universally positionedwithin the intercondylar space of the femoral component and providessubstitutional posterior constraint, as a predesigned compensationfeature for lost posterior cruciate function or for compromisedposterior knee stability. Thus, the possibility of anterior dislocationof the femur is reduced.

Additionally, the cam/follower mechanism is generally positioned betweenthe anterior and posterior femoral condyles and dimensionally spans thefemoro-tibial joint space; protruding into the sector of intercondylarbone within the distal femur; thus, occupying the sector within the kneejoint where the cruciate ligaments are anatomically located. Surgicalselection of a posterior stabilized type of knee prosthesis, therefore,generally predisposes the use of this type device exclusively inclinical situations where the natural posterior (and anterior) cruciateligament structures of the knee joint are absent or sacrificed.

The cam portion of the cam/follower mechanism of the posteriorstabilized device generally includes a convex lobe-shaped surface,integrally machined or cast within a box-like structure known as the"stabilizer box", which in turn, is integrally located between themedial and lateral condyle runners of the femoral component andpositioned between the anterior and posterior condyles. The cam surfaceis generally formed within the posterior wall portion of the stabilizerbox and is bounded by the superior wall on the top, the medial andlateral wall portions on the sides and the anterior wall portion at thefront. The stabilizer box structure, thus formed, occupies a significantenvelope, relative to the overall dimensions of the femoral componentand therefore, requires a substantial resection of viable bone to allowits accommodation within the intercondylar sector of the distal femur.

The articular surface of the posteriorly positioned and anteriorlyoriented convex cam member is generally precisely ground and highlypolished. The convex cam articulates with the anteriorly positioned andposteriorly oriented follower member, as the knee undergoesfemoro-tibial flexion and extension articulation. The mating followersurface is machined integral within the ultra-high molecular weightpolyethylene (UHMWPE) tibial plateau bearing component. The followermember usually consists of a relatively concave articular surfacelocated on the posterior side of an upwardly extending post-likestructure, which is positioned between the concave medial and lateraltibial plateau bearing surfaces.

The post-like structure of the follower member extends upward andgenerally is of sufficient over-all height to span the joint space;thus, protruding into and occupying an appropriate position within thestabilizer box portion for mating with the cam member of thecam/follower mechanism. The cam/follower mechanism, therefore, not onlyfunctionally compensates for lost posterior cruciate function, but alsooccupies essentially the same intercondylar position within the kneejoint; thus requiring that the posterior (and anterior) cruciateligament structures be either absent or sacrificed.

The resultant action of the contacting cam/follower mechanism, thusdescribed, provides posterior stabilization or constraint of the tibialcomponent, relative to the femoral component, generally from aboutmid-range to full range of flexion. Within this limited range,therefore, the posterior stabilizing mechanism essentially simulates thefunctional contribution of the natural posterior cruciate ligamentsattached between the anterior femur and posterior tibia aspects of theknee joint. Additionally, since the cam/follower surface geometry isgenerally non-congruent, the mechanism can be designed to produceposterior femoro-tibial rollback, simulating the biomechanical kinematicdisplacement characteristics of the natural knee joint.

Examples of posterior-stabilized total knee prostheses of the type justdescribed are disclosed in U.S. Pat. Nos. 4,209,861 to Walker; 4,298,992to Burstein et al.; 4,213,209 to Insall et al; and 4,888,021 to Forte etal. Each of the devices described in the above patents incorporates aUHMWPE tibial plateau bearing component with a pair of medial andlateral concave bearing surfaces, and a metal alloy femoral componentwith mating multi-radius condylar runners which ride on the bearingsurfaces. In all cases prosthesis surface geometries approximate thearticular surfaces of the natural knee. The articulation of the femoralcondyles with the tibial plateau bearing surfaces allows primaryfemoro-tibial flexion and extension, and secondary motions of axial andvarus-valgus rotations and anterior-posterior and medial-lateraltranslations. The knee joint reaction forces during primary or secondarymotion are principally supported by the tibial bearing surfaces, and tosome extent by the cam/follower surfaces, and are transferred to theunderlying fixation interfaces and adjacent supportive bone structures.

Additionally, the above referenced designs incorporate a UHMWPE tibialbearing component with an upwardly extending post-like followerstructure, which is positioned between the plateau bearing surfaces,slightly anterior of the component mid-line. The generally concavefollower surface is integrally machined on the posterior side of thecentral post structure. With the femoral and tibial knee components in anormally reduced, surgically implanted position, the upwardly extendingtibial post protrudes into the stabilizer box structure located withinthe intercondylar space of the femoral component. Posterior tibialconstraint is achieved when the posteriorly oriented concave face of thefollower contacts the generally anteriorly oriented convex lobe surfaceof the cam.

Both cam/follower articulation and femoro-tibial articulation occurconcurrently during knee flexion-extension. The commencement ofcam/follower contact, and hence, commencement of posterior stabilizationoccurs on or about mid-flexion range for the devices described in U.S.Pat. Nos. 4,213,209 and 4,298,992, and near the onset of knee flexionfor the devices described in U.S. Pat. Nos. 4,888,021 and 4,209,861. Itshould be noted that however, that there are forces acting over theentire range of motion of the patented devices that are not accountedfor in the patent disclosures.

In each of the above devices, the existence of a relatively largestabilizer box at the mid-portion of the femoral component requiresresection of a significant block of viable intercondylar bone toaccommodate the implantation of the femoral component prosthetic device.Moreover, additional surgical instrumentation is required and thesurgical procedure is somewhat more complicated compared to aconventional condylar-type knee resurfacing device. Additionally, thecam/follower mechanism of the referenced devices essentially occupiesthe same intercondylar position within the knee joint as the cruciateligaments; therefore, the use of these posterior stabilized kneeprostheses are usually surgically indicated in those clinical situationswhere the cruciate ligaments are either absent or incompetent, or suchligaments must be intentionally sacrificed for these prostheses to beimplanted. In other words, these posterior stabilized knee prosthesesgenerally can not be effectively employed to function in conjunctionwith retained, viable posterior (and anterior) cruciate ligamentstructures because of space limitations and impending destructiveinterference with the cam/follower structure.

Furthermore, in each instance, the stabilizer box member has prominent(high profile) medial and lateral side walls and also, anterior andposterior walls. These bounding surfaces can inadvertently contact theupwardly extending tibial post during severe excursions of secondaryknee motion, that is, during axial and varus-valgus rotations andmedial-lateral translation; hence, can function to constrain thesesecondary movements within certain limitations, commensurate with designdimensional clearance. While these devices have been effective inconstraining these types of motion excursions and therefore, effectivein providing a high degree of controlled femoro-tibial stability, theresulting force reactions occurring between the stabilizer box surfacesand tibial post can produce periodic and severe (moment and torque)loading at the tibial component fixation sub-structure interfaces, whichcan cause complications related to component loosening.

Another type of posterior stabilized knee prosthesis is described inU.S. Pat. Nos. 4,892,547 and 4,959,071 to Brown. These designsincorporate a cam/follower mechanism having a low profile and require noresection penalty associated with the accommodation of a protrudingstabilizer box structure. The heights of the tibial follower post(eminence) and the femoral cam members are no greater than the thicknessof the distal and posterior condyles of the femoral component. Therequired femoral resections are thus identical to those of aconventional resurfacing condylar type of knee prosthesis of similarsize and geometric design.

The devices disclosed in these patents however, suffer from otherdisadvantages. First, although the relatively short extending tibialpost is located between the plateau bearing surfaces, the cam member isintegrally incorporated at a high position, between the posteriorcondyles of the femoral component. These knee devices are, therefore,described as "partially stabilized" knee joint prostheses; since, thecam/follower mechanism only comes into contact after flexion ofapproximately 40 degrees has occurred and continues until full flexionis attained. Thus, there is no posterior tibia-to-femur constraint ofthe reconstructed knee joint from the outset of flexion to approximately40 degrees flexion. In this regard, these knee devices are functionallysimilar to other posterior stabilized knee devices, such as thosedisclosed in U.S. Pat. Nos. 4,213,209 and 4,298,992, previouslydiscussed. These patents, therefore, do not take into account the forcesacting over the entire range of motion of the knee joint.

Further with respect to the referenced patents to Brown, when thefollower first contacts the cam surface at approximately 40 degreesflexion, mechanical posterior rollback is initiated due to thedifferences in articular curvature. In a normal knee, physiologicalfemoro-tibial rollback starts at the onset of knee flexion and isgenerally mostly completed by 40 degrees of flexion. This rollback isbelieved to provide substantially a purely rolling motion of thecondyles on the tibial plateau bearing surfaces (femoro-tibial motion),after which there is a transitional motion of rolling and sliding.Therefore, it is desirable that the beginning of cam/follower contactfor initiation of the posterior rollback phase of knee motion occurs asearly as possible in the flexion range, and also that completion ofrollback mostly occurs at or preferably before approximately 40 degreesof flexion is experienced. The '547 and '071 patents furthermoredescribe the action of the cam/follower mechanism of the discloseddevices, in producing posterior rollback, simulating the rolling-type ofposterior displacement of the femoro-tibial articular contact in thenatural knee during knee flexion. However, the indicated commencement ofthis roll-back feature in the '547 and '071 patents "begins afterflexion of the knee joint through approximately 40 degrees (flexion),and ends after flexion of the joint through approximately 90 degrees(flexion)." In the normal knee, through the complex active interactionof the anterior and posterior cruciate ligaments and other surroundingadjacent soft tissue structures, the rollback phase of femoro-tibialarticulation commences early in the flexion range, as aforementioned,and is essentially mostly completed at 40 degrees flexion; with thecharacter of the primary articulation, after completion of posteriorrollback, gradually changing to a gliding and then sliding mode in amanner approaching that of a fixed fulcrum posterior condyle rotation.

Third, the geometry or shape of the articular surface of the cam andfollower members in the '547 and '071 patents are not described as beingcongruent, and therefore, the functional contact area is small and theresultant contact stresses are high when joint loading which tends toproduce anterior dislocation of the femur in imposed. Articular surfacecongruence of the cam and follower member is incorporated in theposterior stabilized device described in U.S. Pat. No. 4,888,021. Thislatter patent utilizes the aforementioned box-like "stabilizer"structure and therefore, requires a large resection of intercondylarfemur bone to accommodate accurate seating of the femoral component. Therelative advantages of large bearing contact surface, associated withjoint prosthesis bearing surface congruency is well known and has beenadopted in a number of prosthetic devices for the knee joint, as well asfor the other joints of the human body, e.g. the shoulder and hip.

Fourth, the referenced cam and follower members, although of limitedheight to prevent intrusion within the intercondylar bone space of thedistal femur, still occupy an intercondylar position of thereconstructed knee joint which, like the other posterior stabilizingknee prostheses previously referenced and described, generally areprincipally prescribed in surgical situations where the cruciateligaments are absent, non-viable and/or are intentionally sacrificed.

In copending application Ser. No. 07/673,790 filed Mar. 22, 1991 by thepresent inventor, a posterior stabilized knee prosthesis construction isdisclosed which distinguished the known prior art in many respects,among them by the provision for cam follower posterior stabilizationinboard of the condyles and attempts by such construction to simulatenormal knee movement and femoral/tibial interaction. Specifically, thecondyles of the respective components rotate and the tendency for thefemoral component to move anteriorly during full flexion is prevented bythe cam/follower and support.

This construction, however, possesses a drawback, as the cam support andposterior stabilization is disposed inboard of the condyles and therebycuts off the ability to retain any of the original ligamenture in theinstance where surgical removal of less radical nature is possible. Aneed therefore exists for a posterior stabilized knee construction thatcan accommodate the retention of certain of the original jointstructures while providing the stability, support and longevity of thenatural knee.

With regard to hinged knee prostheses, mechanically linked or hingedtype of knee prostheses generally provide a fixed fulcrum or uni-axisflexion-extension capability. Some of these devices are fullyconstrained in axial rotation, while others provide either partiallyconstrained or unconstrained axial rotational freedom. Hinged kneeprostheses are surgically indicated in selective cases involving grossand unreconcilabie knee joint instability; resulting from majordestruction and incompetency of the surrounding soft tissue structuresdue to previous surgical failure, trauma, disease and congenital relatedconditions. Mechanical linking of the femoral and tibial prostheticcomponents by means of a hinge pin connection or some otherbearing/connection means functionally compensates for loss ofbiomechanical knee constrainment and stability; which, is normallyprovided by the soft-tissue structures surrounding the knee joint.

Examples of uni-axis hinged type knee prosthetic devices are disclosedin U.S. Pat. No. 3,996,624 to Noiles and U.S. Pat. No. 4,136,405 toPastrick et al. The Noiles and Pastrick et al inventions additionallyprovide partially constrained femoro-tibial axial rotation (rotatingplatform concept) with minimal medial-lateral or varus-valgus rotation.Further, the prosthesis disclosed in U.S. Pat. No. 3,837,009 to Walkerprovides variable axis flexion/extension motion but within the verticalor coronal plane of the knee joint and in a manner which does notinvolve natural-like posterior femoro-tibial rollback. A verticallyoriented tear-drop shape slotted hole in the upwardly extending tibialpost provides only vertical displacement of the femoro-tibial instantcenter, as a function of the multi-radius shape of the femoral condyles.Distal divergence of the vertical slotted hole provides radial clearancefor the transverse hinge pin to allow slight axial rotational freedomand slight anterior-posterior freedom, over the latter stages of kneeflexion. No provisions are incorporated in the Walker design to producenatural-like femoro-tibial posterior rollback nor posterior and anteriorstabilization of knee joint motion.

It is therefore apparent that even hinged constructions suffer from theinability to simulate natural motion of the tibia and femur with respectto each other throughout the full range of knee motion encountered ineveryday activity, and that a need therefore exists for a hingedconstruction that remedies the aforenoted deficiencies.

OBJECTS AND SUMMARY OF THE INVENTION

In view of the above, the present invention provides knee prostheses ofsignificant versatility, that are capable of a broad range of functionalcapabilities. All of the prostheses presented herein are able to serveas resurfacing type prostheses according to the first category of totalknee protheses, where the posterior (and anterior) cruciate ligamentsare viable and retained. Additionally, the inventive prostheses are ableto function as posterior stabilized total knee prosthetic devicesaccording to the third category, where, the posterior cruciatestructures are absent, incompetent or intentionallysacrificed--providing in all instances posterior stabilization from theonset of femoro-tibial flexion and continuing throughout the fullflexion range. The present invention offers prostheses meeting thecriteria of the second category that include a mechanical hingedconnection between the femoral and tibial components.

A central aspect of all of the prosthetic devices of the presentinvention is the location of the cam and follower means that participatein providing posterior stability, on the outboard lateral aspects of therespective femoral and tibial components. In the first describedembodiment, the central area medial to the femoral condyles and thetibial plateau bearing surfaces, respectively, as described herein, isempty, so that any retained natural joint structures such as ligamenturemay pass unobstructed therethrough. Accordingly, such device can be usedin surgical situations where the long term status of the posteriorcruciate ligament structures cannot be reliably ascertained,preoperatively or interoperatively, because of possible continuation ofthe disease process, overstressing of the ligament structures byimproper component design or malalignment, inadvertent or accidentalsurgical damage, or the like. In the event that the viability of theposterior cruciate ligament structures deteriorates postoperatively dueto uncertain pathological, physiological or design related etiology,this first construction of the present invention will continue toprovide uninterrupted knee joint function and posterior stabilizationwithout surgical intervention, as its design specifically accommodatesboth the presence and the absence of the posterior (and anterior)cruciate structures.

Also, the selected geometry and outboard position of the cam andfollower members of all of the present prostheses can produce a morenatural-like posterior rollback displacement of the femoro-tibialarticulation, commencing from the onset of flexion, including theaccommodation of maximum hyperextension, and proceeding in a uniformmanner to approximately 30 degrees flexion, where rollback isessentially completed.

Upon completion of the rollback phase, the cam member function isuniquely transferred to the outboard portion of the medial and lateralposterior femoral condyles, and the follower member function istransferred to the outboard portion of the respective concave arcuateposterior tibial plateau bearing surfaces--and then traversing back(flip-flop) onto respective surfaces of the concave arcuate followermember, as the flexion angle increases from approximately 30 degreesflexion to full flexion. After completion of posterior rollback,therefore, until the attainment of full flexion, the posterior femoralcondyles and mating posterior tibial plateau bearing surfaces provide aconcurrent dual functionality: namely, (1) to provide primaryfemoro-tibial knee joint articulation; and (2) to provide posterior(tibia-to-femur) stabilization. In this manner posterior stabilizationcontinues to occur throughout the entire flexion range; thus, reducingthe possibility of anterior dislocation of the femur. Likewise duringthis flexion phase, the ensuing congruent contact of the posteriorfemoral condyles with the tibial plateau bearing surfaces and followermember surfaces also provides anterior stability; thus, reducing thepossibility of posterior dislocation of the femur.

Furthermore, the aforementioned ensuing flip-flop (second phase)cam/follower function, between the outboard portion of the medial andlateral posterior femoral condyles and respective posterior portions ofthe concave arcuate tibial plateau bearing surfaces and concave arcuatefollower member surfaces, as discussed in detail later on, results in anet increase in articular bearing contact area, which is additive to thefemoro-tibial articular bearing contact area, increasing proportionallywith the flexion angle from approximately 30 degrees flexion toapproximately 55 degrees flexion; where, maximum articular bearingcontact area is achieved. From 55 degrees to full flexion, the resultingnet effective femoro-tibial bearing surface area is maintained at themaximum level tending to functionally augment the transfer, maintenanceand distribution of the higher levels of knee joint loading associatedwith increased flexion. This is totally unlike conventional resurfacingtotal knee prostheses (first category) and posterior stabilized totalknee prostheses (third category), which generally incorporatenon-congruent or "line" contact articular bearing contact patterngeometries in both the femoro-tibial joint and cam/follower mechanism.

The stabilizer cam and follower members that serve as the primaryarticular bearing surfaces of the present invention are of low profiledesign and are effectively integrated--not within the conventionalintercondylar space--but within the outboard anterior-central sector ofthe medial and lateral distal femoral condyles. In this manner the needfor a "stabilizer box", together with all of its associated potentialclinical and functional shortcomings, is avoided. With the integrationof the cam/follower mechanism within the dimensional thickness boundaryof the distal femoral condyles, the intercondylar space is unobstructedand therefore, does not require intercondylar bone resection toaccommodate the femoral component. Furthermore, the intercondylar spaceis especially free to accommodate the implantation of the kneeprosthesis components of the present invention within a compromised kneejoint in the presence of retained viable, retained questionably viable,absent, resected incompetent or resected viable posterior (and anterior)cruciated ligament structures.

In accordance with a further embodiment of the invention, a hingedprosthesis is provided that draws upon the structural advantages of theoutboard cam/follower construction hereof, in combination with aninnovative hinge connection between the femur and tibia. The hinge meansincludes a second cam and follower means within the intercondylar spacethat functions as an ancillary load bearing articular structure thatassumes some of the impact and loading that the knee joint experiencesin motion, and thereby lessens the forces and associated wear that areimposed on the articulating surfaces with the condyles.

Accordingly, it is a principal object of the present invention toprovide a total knee prosthesis that has dual clinical applicability,either as a resurfacing total knee prosthesis with functionalaugmentation of retained posterior (and anterior) cruciate ligamentstructures, or as a posterior stabilized knee prosthesis with functionalcompensation for lost or surgically removed posterior (and anterior)cruciate ligament structures.

It is another object of the present invention to provide a total kneeprosthesis as aforesaid that offers posterior stabilization of the kneejoint--with or without posterior (and anterior) cruciate ligamentstructures--from the onset of knee flexion and throughout the completerange of flexion.

It is another object of the present invention to provide a total kneeprosthesis as aforesaid in which the articulating cam/follower membersproduce a posterior displacement or rollback function of thefemoro-tibial joint in a similar manner as the natural knee.

It is still another object of the present invention to provide a totalknee prosthesis as aforesaid that provides congruent contact of themedial and lateral posterior femoral condyles with the respectiveposterior tibial plateau bearing surfaces and follower member surfaces,and that continues after posterior rollback is completed.

It is a still further object of the present invention to provide a totalknee prosthesis as aforesaid that requires no additional femoral andtibial bone resectioning compared to a conventional condylar-typeresurfacing or non-posterior stabilizing type of total knee prosthesisof similar component size.

It is yet a further object of the present invention to provide a totalknee prosthesis as aforesaid that closely mimics the naturalbiomechanics of the knee joint as it relates to posterior rollback ofthe femoro-tibial joint during flexion of the knee.

It is still another object of the present invention to provide a totalknee prosthesis as aforesaid in which the follower surface member meansare always in contact with the respective cam member surface means,providing posterior stabilization throughout the entire flexion range ofthe prosthetic knee joint.

It is yet another object of the present invention to provide a totalknee prosthesis as aforesaid that defines a hinge connection therein toaccommodate total absence of supporting ligamenture.

It is another object of the present invention to provide a total hingedknee prosthesis as aforesaid wherein a hinge is provided that offersimproved simulation of natural motion even in hyperextension.

It is another object of the present invention to provide a total hingedknee prosthesis as aforesaid wherein the hinge also defines cam andfollower means to accept and distribute the forces imposed on theprosthesis during motion.

It is yet another object of the present invention to provide a totalknee prosthesis as aforesaid in which the femoro-tibial joint articularsurfaces and the cam-follower member articular surfaces, because of therelatively large contact surface areas therein, can be fabricated froman appropriately compatible ceramic-ceramic, e.g. high density alumina;metal-metal, e.g. cobalt-chrome alloy; or ceramic-metal articularbearing couple.

It is therefore an object of this invention to provide a total kneeprosthesis device as aforesaid offering the above features andassociated, potential clinical advantages.

These and other objects are achieved in a knee joint prosthetic device,which is comprised of a femoral component, a tibial component andpatellar component, suitably designed to restore knee joint functionwhen surgically implanted in the conventional manner to the preparedends of the femur and tibia, respectively.

The femoral component incorporates a pair of medial and lateral condylarrunners, which like the natural counterparts are spatially separated andare of multi-radius geometry. Furthermore, the medial and lateralanterior femoral condyles are integrally interconnected by a flangeportion (pateliar flange), which provides an articular bearing surfacefor the resurfaced femoro-patellar joint. The femoral component iscomprised essentially of two distinct articular bearing portions: (1)the femoro-tibial joint portion consisting of the medial and lateralanterior condyles, the inboard portion of the medial and lateral distalcondyles and the inboard portion of the medial and lateral posteriorcondyles; and (2) the cam member portion, which is integrated withineach distal femoral condyle, consisting of an anterior concave surfaceportion and a posterior convex cam surface portion. Additionally, afterapproximately 30 degrees flexion to full flexion, the outboard portionof the medial and lateral posterior femoral condyles assumes a dualfunctional role; namely as a cam member to provide posterior (andanterior) stabilization and also as an articular member of thefemoro-tibial joint to provide primary flexion-extension and secondaryrotational and translational motions. The continuous surface geometryand coincident center and radius of curvature of the inboard andoutboard portions of the posterior femoral condyles allows biomechanicalsharing of articular bearing contact area between the cam/followermechanism and femoro-tibial joint and hence, sharing of the transfer,sustainment and distribution of imposed joint forces acting across thereconstructed knee joint.

The total prostheses of the present invention are able to simulatenatural knee motion and provide increased service due to severalcharacteristics of the construction. For example, after rollback iscompleted at approximately 30 degrees flexion, the cam member functionis transferred from the convex cam member surface integrated within thecentral-posterior portion of the medial and lateral distal femoralcondyles to the outboard portion of the medial and lateral posteriorfemoral condyles, and the follower member function is transferred fromthe medial and lateral outboard concave arcuate follower member surfacesto the outboard medial and lateral posterior portion of the concavearcuate tibial plateau bearing surfaces. As the flexion angle increases,the articular path of the outboard-anterior portion of the medial andlateral posterior condyles traverses anteriorly, commencing congruentarticulation with the concave arcuate surface of the medial and lateralfollower members.

Further, after rollback is completed at approximately 30 degreesflexion, the outboard-anterior portion of the medial and lateralposterior femoral condyles articulates with the outboard portion of therespective concave arcuate posterior tibial plateau bearingsurfaces--with the congruent articular path traversing anteriorly,retracing back onto to the respective medial and lateral concave arcuatefollower member surfaces, as flexion angle increases to full flexion.This action provides (1) supplementary femoro-tibial joint articularsupport, and (2) posterior and anterior stabilization of the knee joint.This flip-flop articular path also results in an increase in articularbearing surface area of the cam/follower members, which is additive tothe articular bearing surface area of the femoro-tibial joint,increasing proportionally with flexion angle to approximately 55degrees, where maximum articular bearing surface area is attained. Themaximum surface area is maintained throughout the remainder of theflexion range to full flexion, to functionally augment the transfer,maintenance and distribution of the higher levels of femoro-tibial jointloading associated with higher levels of knee flexion.

As used herein, the terms "inboard" and "outboard" are intended todescribe the location of the cam member and follower means in relationto the condyles of the femoral component and the plateau regions of thetibial component. Particularly, "inboard" represents a position that ismedially and laterally adjacent to the intercondylar space of thefemoral component and the central eminence of the tibial component,while "outboard" refers to the locations at the extreme medial andlateral positions of the knee joint.

An intercondylar space or opening within the condyles is formed by theposterior edge of the distal portion of the patella flange at thejunction of the anterior and distal condyles, and the medial and lateraledges of the respective lateral and medial femoral condyles. Unlike mostconventional posterior stabilized total knee prostheses, theintercondylar opening portion of the present knee prosthesis inventionwithin the region, thickness and plane of the respective condylarboundaries is spatially unobstructed--like conventional posteriorcruciate retaining or anterior and posterior cruciate retaining condylarresurfacing types of knee prosthesis designs (of the first category).Hence, the knee design according to the present invention can besurgically employed in clinical situations embracing both sets ofsurgical indications currently established and accepted for bothcondylar resurfacing and posterior stabilized types of total kneeprostheses.

The interconnecting eminence extends into the intercondylar opening,anteriorly and centrally, but not above the thickness of the distal orposterior femoral condyles of the femoral component. Since its maximumheight is not greater than the thickness of the distal or posteriorfemoral condyles, resection of additional distal femur bone to provideadequate clearance for the height of the eminence is, therefore, notrequired. The resulting unobstructed spacial design of the region in andabout the intercondylar space of the femoral component and theincorporation of an appropriate conventional cruciate "cut-out" locatedposterior of the interconnecting eminence and between the inboard medialand lateral tibial plateau bearing surfaces, will provide the requiredclearance for surgically retained posterior (and anterior: deepercut-out required) cruciate ligament structures; which, constitutes asurgical alternative--not provided by the more conventional types ofposterior stabilized total knee prostheses (third category).

The articular surface geometry of the medial and lateral centrallypositioned concave arcuate follower member portion has an identicalposition, profile shape and radius and center of curvature as theinboard and outboard posterior portions of the respective tibial plateaubearing surface members. In the preferred embodiment, the medial andlateral convex cam member contacts the respective centrally positionedconcave arcuate follower member surface at the onset of flexion andremains in non-congruent articular contact as the flexion angleincreases to approximately 30 degrees flexion. From approximately 30degrees flexion to full flexion both posterior (and anterior)stabilization and femoro-tibial articulation is provided by the dualfunctional role assumed by the posterior femoral condyles, coming intocongruent contact with the inboard and outboard posterior portions ofthe tibial plateau bearing surfaces and also with the centrallypositioned concave arcuate follower member surfaces. Thus, posteriorstabilization occurs over the entire flexion-extension range of thereconstructed knee joint.

At the outset of flexion, the ensuing contact of the medial and lateralconvex cam members with the respective centrally positioned concavearcuate follower surface members produces a camming action whichdisplaces the center of curvature of the posterior femoral condyles,posteriorly and toward the center of curvature of the anterior concavearcuate follower members and the inboard and outboard concave arcuateposterior portion of the tibial plateau bearing surfaces; thus,producing a natural-like posterior rollback displacement of the condylesof the femoral component relative to the plateau bearing surfaces of thetibial component. At approximately 30 degrees flexion, the center ofcurvature of the posterior femoral condyles meets and coincides with thecenter of curvatures of the concave arcuate follower members andposterior portion of the tibial plateau bearing surfaces to completeposterior rollback of the femoro-tibial joint; hence, the inboardfemoro-tibial condylar bearing surfaces and the cam/follower memberarticular bearing surfaces coincidentally assume a condition ofcongruent contact after rollback is completed. From this point in theflexion range, (30 degrees flexion) to full flexion, both articularelements will maintain contact congruency. As will be discussed in moredetail later on, the net articular bearing contact area of thefemoro-tibial joint attains a maximum value at approximately 30 degreesflexion and maintains this level of articular contact area at a constantvalue over the remainder of the flexion range. The congruent articularbearing contact area of the cam/follower members increasesproportionally with flexion angle from approximately 30 degrees flexionand reaching a maximum value at approximately 55 degrees flexion. Fromthis point in the flexion range to full flexion, the net articularsurface area of the cam and follower members--which is additive to thefemoro-tibial articular bearing contact surface area--remains constantat the maximum value.

Additionally, as another principal embodiment of the present invention,from the point in the flexion range where femoro-tibial rollback iscompleted at approximately 30 degrees flexion to full flexion, theoutboard portion of the medial and lateral posterior condylesmechanically "link-up" or commence articulation with the articularsurface of the respective follower members; thus functioning thereon asthe medial and lateral cam members. The inboard portion of the medialand lateral posterior condyles remain in congruent contact with theinboard posterior portion of the medial and lateral tibial plateaubearing surfaces within this flexion range (30 degrees to full flexion)in the usual manner to provide primary flexion-extension femoro-tibialarticulation.

As still another embodiment of the present invention, the resultingmedial and lateral posterior condyle/follower member articular contact,as described, provides posterior and anterior knee joint stabilizationwithin this flexion range and also, uniquely provides additionalfemoro-tibial articular bearing surface area, which proportionallyincreases in magnitude as flexion angle increases, up to approximately55 degrees flexion. Further, as the radius of curvature of the medialand lateral posterior condyles is identical to the radius of curvatureof the medial and lateral concave arcuate follower members and inboardand outboard posterior portions of the medial and lateral tibial plateaubearing surfaces, the resulting posterior condyle/follower membercongruent articular bearing contact area compliments, augments and worksin conjunction with the congruent femoro-tibial condylar articularbearing contact area from about 30 degrees flexion, to fullflexion--increasing proportionally with flexion angle up to about 55degrees and remaining at this level, thereafter to full flexion. In thisway, a large net effective femoro-tibial joint articular bearing contactarea is provided, that for the present invention with intermediate sizedknee prosthesis components is equivalent to a 32 mm femoral (hip) head.Large articular contact area is known to reduce contact stresses andassociated plateau (and follower member) bearing surface wear anddamage, and the potential accompaniment of improved in-situ knee implant(UHMWPE) bearing service life.

Required bone resection at the anterior, distal and posterior aspects ofthe distal femur to allow accurate seating of the femoral and tibialcomponents of the present invention is essentially consistent to theresection requirements of most conventional condylar resurfacing typesof knee prostheses. This feature is provided, since the height of themedial and lateral cam and follower members of the stabilizer mechanismis designed to be within the maximum thickness of the distal andposterior condyles of the femoral component. The resulting potentialclinical advantage relates to enhanced surgical versatility, associatedwith selecting for implantation a knee prosthesis which embraces thesurgical indications of either a condylar resurfacing type or posteriorstabilized type of total knee prosthesis with minimal femoral and tibialbone resection, e.g. without requiring the resection of a substantialblock of intracondylar distal femur bone to accommodate a conventional"stabilizer box". Additionally, minimal femoral and tibial boneresection, during knee joint reconstruction, is universally recognizedas a desirable surgical alternative for a number of obvious clinicalreasons--one of which relates to the presence of stronger and denserbone stock at levels closest to the condylar surface, and the other ofwhich relates to greater retained bone mass and associated potentiallyeasier surgical course in the event implant revision is required at alater date.

In a further aspect, the UHMWPE tibial bearing component of the presentinvention is designed to provide both condylar resurfacing and posteriorstabilization. In conventional knee prosthesis systems the UHMWPE tibialplateau bearing component for a resurfacing condylar type of kneeprosthesis is unique or different than one which is designed forposterior stabilization. The femoral component exhibits a similarinterchangeability limitation. The dual functionality of the presentinvention could result in less overall system complexity and reducedimplant inventory requirements. Surgical instrumentation can also besignificantly simplified; since, the various (and numerous) alignmentfixtures, resection guides, provisional trial components, etc., canreadily accommodate both condylar resurfacing and posterior stabilizedtypes of knee joint reconstructions.

In accordance with a first aspect of the present invention, a kneeprosthesis capable of providing resurfacing to the adjacent ends of theexisting bone structures, as well as total posterior stabilization tothe knee joint, is provided that comprises:

a) a femoral component including:

i) a medial condyle having an anterior portion, a distal portion and aposterior portion;

ii) a lateral condyle having an anterior portion, a distal portion and aposterior portion;

iii) an anterior patella flange interconnecting the anterior portions ofthe medial and lateral condyles in parallel, spaced apart relation; and

iv) cam member means integral with said medial and lateral condyles andlocated outboard thereof, said cam member means having an anteriorlylocated concave cam member surface and a posteriorly located convex cammember surface;

b) a tibial component including:

i) multi-radius tibial plateau bearing surface means for receiving saidmedial and lateral condyles for rolling and sliding movement thereon;and

ii) follower member means integral with said bearing surfaces forreceiving the cam surfaces of said cam member means for rotational andsliding movement thereon; and

c) the cam member surfaces of said cam member means being in contactwith said follower member means for substantially the entire flexionrange of the reconstructed knee joint.

In accordance with another aspect of the present invention, a total kneeprosthesis is provided that comprises:

a) a femoral component including:

i) a medial condyle having an anterior portion, a distal portion and aposterior portion;

ii) a lateral condyle having an anterior portion, a distal portion and aposterior portion;

iii) an anterior patella flange interconnecting the anterior portions ofthe medial and lateral condyles in parallel, spaced apart relation; and

iv) cam member means integral with said medial and lateral condyles andlocated outboard thereof, said cam member means having an anteriorlylocated concave cam member surface and a posteriorly located convex cammember surface;

b) a tibial component including:

i) multi-radius tibial plateau bearing surface means for receiving saidmedial and lateral condyles for rolling and sliding movement thereon;and

ii) follower member means integral with said bearing surfaces forreceiving the cam surfaces of said cam member means for rotational andsliding movement thereon; and

c) said convex cam member surface being in sliding contact with saidfollower member means to provide posterior rollback of said condyles onsaid tibial plateau bearing surface means during flexion, starting atstarting at the outset of flexion (approximately maximum normalhyperextension of flexion), and being completed at an angle less thanapproximately 40 degrees (approximately 30 degrees) of flexion.

In a still further aspect of the present invention, a knee prosthesiscapable of providing resurfacing to the adjacent ends of the existingbone structures, as well as total posterior stabilization to the kneejoint, is disclosed which comprises:

a) a femoral component including:

i) a medial condyle having an anterior portion, a distal portion and aposterior portion;

ii) a lateral condyle having an anterior portion, a distal portion and aposterior portion;

iii) an anterior patella flange interconnecting the anterior portions ofthe medial and lateral condyles in parallel, spaced apart relation; and

iv) a cam member means integral with said medial and lateral condylesand located outboard thereof said cam member means having an anteriorlylocated concave cam member surface and a posteriorly located convex cammember surface;

b) a tibial component including:

i) multi-radius tibial plateau bearing surface means for receiving saidmedial and lateral condyles for rolling and sliding movement thereon;and

ii) follower member means integral with said bearing surfaces forreceiving the cam surfaces of said cam member means for rotational andsliding movement thereon; and

c) the outboard portion of the medial and lateral posterior femoralcondyles being in congruent contact with the outboard posterior portionof the tibial plateau bearing surface means at the completion ofposterior rollback at approximately 30 degrees flexion and thenretracing back anteriorly to the centrally positioned concave arcuatefollower member means, as flexion angle increases from approximately 30degrees flexion to full flexion.

In a still further aspect of the invention, a total knee prosthesiscapable of providing resurfacing to the adjacent ends of the existingbone structures, as well as total posterior stabilization to the kneejoint, is disclosed that comprises:

a) a femoral component including:

i) a medial condyle having an anterior portion, a distal portion and aposterior portion;

ii) a lateral condyle having an anterior portion, a distal portion and aposterior portion;

iii) an anterior patella flange interconnecting the anterior portions ofthe medial and lateral condyles in parallel, spaced apart relation; and

iv) cam member means integral with said medial and lateral condyles andlocated outboard thereof, said cam member means having an anteriorlylocated concave cam member surface and a posteriorly located convex cammember surface;

b) a tibial component including:

i) multi-radius tibial plateau bearing surface means for receiving saidmedial and lateral condyles for rolling and sliding movement thereon;and

ii) follower member means integral with said bearing surfaces forreceiving the cam surfaces of said cam member means for rotational andsliding movement thereon; and

c) hinge means associated with and hingably connecting said femoralcomponent and said tibial component;

d) the cam member surfaces of said cam member means being in contactwith said follower member means for substantially the entire flexionrange of the knee.

Still further, the present invention extends to a hinge assembly for usein a knee prosthesis adapted to provide hingeable connection between afemoral component and a tibial component of such knee prosthesis, and tooffer posterior stabilization thereto, said hinge assembly comprising:

a) plural spaced apart femoral hinge components;

b) a tibial hinge component located between said femoral hingecomponents;

c) a hinge axis comprising a hinge pin extending between said femoralhinge components and said tibial hinge components;

d) hinge-related posterior stabilization means comprising cam meansdefined by said tibial hinge component and follower means defined bysaid femoral hinge components.

The above and other objects, features and advantages of the presentinvention will become apparent from the following detailed descriptionof the invention, when considered in conjunction with the accompanyingdrawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a front elevational view of a prosthesis according to an firstembodiment of the present invention, partly exploded for clarity.

FIG. 2 is a medial side elevational view of the knee prosthesis of FIG.1, shown with all components in reduced or assembled mode, with theanterior aspect being to the left and the posterior aspect being to theright of the drawing;

FIG. 3 is a rear (posterior) view of the prosthesis of FIG. 1, shownwith all components in reduced or assembled mode, with the right side ofthe drawing being lateral;

FIG. 4 is a front (anterior) view of the femoral component of kneeprosthesis of FIG. 1, showing the positional relationship of the patellaflange, the anterior aspects of the medial and lateral condyles, theinboard distal femoral condyles and the outboard cam member meansintegrated within the medial and lateral distal femoral condyles, withthe left side of the drawing being lateral;

FIG. 5 is a medial side elevational view of the femoral component ofFIG. 4, showing the medial cam member means integrally incorporatedwithin the dimensional thickness of the medial distal femoral condyle,consisting of a concave surface anteriorly and the convex cam memberposteriorly, with the anterior aspect being to the left of the drawing;

FIG. 6 is a top plan view of the femoral component of FIG. 4, showingthe obvious absence of a conventional intercondylar "stabilizer box" andthe spatially unobstructed design of the intercondylar space, with theanterior aspect being to the lower side of the drawing and the lateralaspect being to the left of the drawing;

FIG. 7 is a bottom plan view of the femoral component of FIG. 4, showingthe positional relationship of the inboard femoral distal condyles andthe cam member means integrally incorporated within the outboard portionof the medial and lateral distal femoral condyles, with the anterioraspect being to the top and the lateral aspect being to the left of thedrawing;

FIGS. 8a-8c are medial side (exploded) elevational views of the tibialcomponent of the knee prosthesis of FIG. 1, showing the mode ofassembly, dovetail channel assembly constrainment and screw securementof the UHMWPE tibial plateau bearing component with the mating tibialbase component, with the anterior aspect being to the left and medialaspect being the forward or frontal view of the drawing; FIG. 8b is aside elevational view of the medial side view of the UHMWPE tibialplateau bearing component showing the multi-radius articular geometry ofthe inboard femoro-tibial surface means and the outboard follower membermeans consisting of the anterior convex surface member and the centrallypositioned concave arcuate follower surface member with connectinginboard (and outboard) posterior portion of the tibial plateau bearingsurface means.

FIG. 9 is a top plan view of the UHMWPE tibial plateau bearing componentshown in FIG. 8b, showing the positional relationship of the inboardfemoro-tibial condylar bearing surfaces, interconnecting centraleminence with screw port, the outboard follower member means and theposteriorly situated posterior cruciate clearance cut-out (an anteriorcruciate cut-out would be deeper, anteriorly), with the left side of thedrawing being anterior and the upper side of the drawing being lateral;

FIG. 10 is a bottom plan view of the UHMWPE tibial plateau bearingcomponent shown in FIG. 8b, showing the layout of the peripheral andcentral constraining dovetail channels and anterior location of thescrew thread clearance port, with the left side of the drawing teeinganterior and the lower side of the drawing being lateral;

FIG. 11 is a top plan view of the tibial base component as shown in FIG.8a, showing the posterior cruciate ligament clearance cut-out andrelative positions of the peripheral and central constraining dovetailchannels, with the left side of the drawing being anterior and the upperside being lateral;

FIG. 12 is a bottom plan view of the tibial base component shown in FIG.8a, showing the porous coating means, intramedullary stem withstabilizing gussets and stabilizing fixation pegs, with the left side ofthe drawing being anterior and the lower side being lateral;

FIG. 13 is a medial side elevational view of the knee prosthesis shownin FIG. 1--except the femoral component and tibial plateau bearingcomponent are depicted in reduced relative position at the outset offlexion at 6 degrees of hyper-extension, with the left side of thedrawing being anterior and the right side being posterior;

FIG. 14a-14e are medial side elevational views of the knee prosthesisshown in FIG. 1, where the femoral component and tibial plateau bearingcomponent are depicted in several reduced relative functional positionscorresponding to the outset of flexion at 0 degrees flexion, anintermediate position at 15 degrees flexion prior to completion ofposterior femoro-tibial rollback, completion of posterior rollback atapproximately 30 degrees flexion, attainment of maximum cam/followerarticular bearing contact area at approximately 55 degrees flexion, andat 120 degrees maximum flexion are shown to demonstrate thebiomechanical interaction of the components and the congruent path ofarticular mechanics of the outboard medial (and lateral) cam/followermechanism--shown by the solid triangles--and of the inboard medial (andlateral) femoro-tibial joint--shown by the empty triangles.

FIG. 15 is a front (anterior) elevational view of a mechanically linkedvariable axis total knee prosthesis 110 according to an embodiment ofthe invention in which the femoral component 112 is depicted reducedwith the tibial component 114 being comprised of the tibial plateaubearing component 157 assembled onto the tibial base component 184. Itshould be noted that a right-side knee prosthesis is shown, in which theleft side is the lateral aspect and the front view is the anterioraspect. A total knee prosthesis for left-side knee arthroplasty wouldincorporate a femoral component, a mirror image of that shown in FIG. 15in which the right side would be the lateral aspect. The tibial plateaubearing component 157 and the tibial base component 184 aresymmetrically designed and hence, universally applicable to both rightand left-side femoral components of comparable size;

FIG. 16 is a medial side elevational view of the total knee prosthesisof FIG. 15, shown with all components in reduced or assembled position,with the anterior aspect being to the left and the posterior aspect tothe right;

FIG. 17 is a rear (posterior) elevational view of the total kneeprosthesis of FIG. 15, shown with all components in reduced or assembledposition, with the right side of the drawing being lateral;

FIG. 18 is a front (anterior) elevational exploded view of the totalknee prosthesis of FIG. 15, showing femoral component 112 in assemblyalignment with the tibial component 114 and hinge pin 115. The left sideof the drawings being the lateral aspect and the frontal view beinganterior.

FIG. 19 is a front (anterior) elevational view of the femoral componentof the total knee prosthesis of FIG. 15, showing the positionalrelationship of the patella flange 136, the anterior aspects 128 and 130of the medial and lateral femoral condyles 116 and 118, the medial andlateral inboard distal femoral condyles 124a and 126a and the medial andlateral outboard cam member means 132, with the left side of the drawingbeing lateral;

FIG. 20 is a medial side elevational view of the femoral component ofFIG. 19 showing the medial outboard cam member means 132 being comprisedof a concave portion 132b anteriorly and convex cam member portion 132aposteriorly, integrally incorporated within the outboard portion ofmedial distal femoral condyle 124 with the convex cam member portion132a in smooth transition with the outboard portion 120b of the medialposterior femoral condyle 120, with the anterior aspect being to theleft of the drawing;

FIG. 21 is a top plan view of the femoral component of FIG. 19 showingfixation surfaces: anterior 140, anterior-distal 142a and 142, distal144 and 146, posterior 152 and 154 and central surfaces 125, 127 and 131with metallurgically applied porous surface structure means 156; andcentrally positioned intercondylar housing 137 with intermedullary stem139, which interconnects the lateral surface aspect 116a of medialfemoral condyle 116 and the medial surface aspect 116b of lateralfemoral condyle 118, with the anterior aspect being to the lower side ofthe drawing and the lateral aspect being to the left;

FIG. 22 is a bottom plan view of the femoral component of FIG. 19showing the positional relationship of the medial and lateral inboarddistal femoral condyles 124a and 126a with the respective anteriorcondylar aspects 128 and 130, with the inboard portions 120a and 122aand outboard portions 120b and 122b of respective posterior condyles 120and 122, with the cam member means 132 integrally incorporated withinthe outboard portion of the medial and lateral distal femoral condyles124 and 126 and with the interior surface portions 129, 116a and 116b ofthe centrally positioned interconnecting intercondylar housing 137 withthe anterior aspect being to the top of the drawing and the lateralaspect being to the left;

FIGS. 23a-23c are medial side (exploded) elevational views of tibialcomponent 114 of the knee prosthesis of FIG. 15 showing assemblyalignment, mode of dovetail channel 183 and 183a engagement and screw193 securement means of the tibial plateau bearing component 157 withthe mating tibial base component 184 and threaded assembled tibial endplug 189; additionally depicted are the multi-radius articular geometryof the inboard femoro-tibial bearing surface means 158, the slottedtransverse port 115d with anterior center-axis O and posteriorcenter-axis O' for hinge pin 115 assembly and the outboard followermember means 176 consisting of anterior convex surface portion 178a andcentral concave arcuate follower surface portion 178, smoothly connectedposteriorly to the outboard and inboard portions of the posterior tibialplateau bearing surface means 162a and 162 with the anterior aspectbeing to the left of the drawing and the medial aspect being the frontview.

FIG. 24 is a top plan view of the tibial plateau bearing component 157shown in FIG. 23c, showing the positional relationship of the inboardtibial plateau bearing surfaces 158 and 160, centrally positionedinterconnecting tibial post 174 with screw port 175 and outboardfollower member means 176 with the left side of the drawing beinganterior and the upper side being lateral, relative to the assemblyorientation of the total knee prosthesis of FIG. 15;

FIG. 25 is a bottom plan view of the tibial plateau bearing component157 in FIG. 23c, showing the layout of the side posterior peripheral andcentral engaging dovetail channels 183a integral with supporting surface177 and anterior location of the screw thread clearance port 175 withthe left side of the drawing being anterior and the lower side of thedrawing being lateral relative to assembly orientation of FIG. 15;

FIG. 26 is a top plan view of the tibial base component 184 in FIG. 23a,showing the relative positions of the side-posterior peripheral andcentral engaging dovetail channels 183 and anterior-central threadedscrew port 187 with the left side of the drawing being anterior and theupper side being lateral relative to assembly orientation of FIG. 15;

FIG. 27 is a bottom plan view of the tibial base component 184 in FIG.23a, showing the porous coated fixation surface means 188 in partialsection, intramedullary stem 191 with stabilizing gussets 192 andstabilizing fixation pegs 190 with the left side of the drawing beinganterior and the lower side being lateral relative to assemblyorientation of FIG. 15;

FIGS. 28a-28e are (mirror image) sectional views of the total kneeprosthesis shown in FIG. 15 through Section A--A, where the articularmechanics of the lateral (similarly the medial) outboard cam/followermechanism are depicted at several functional positions corresponding tothe outset of flexion at 0 degrees flexion (FIG. 28a), an intermediateposition at 10 degrees flexion (FIG. 28b), completion of posteriorfemoro-tibial rollback at approximately 25-30 degrees flexion (FIG.28c), attainment of maximum cam/follower bearing contact area atapproximately 75 degrees flexion (FIG. 28d) and at 135 degrees maximumflexion (FIG. 28e) and where the extent of cam/follower bearing contactarea being indicated by the A-P contact length, as shown by solidtriangles with the anterior aspect being to the left and posterior tothe right;

FIGS. 29a-29e are (mirror image) sectional views of the total kneeprosthesis shown in FIG. 15 through Section B--B, where the articularmechanics of the inboard lateral (and medial) femoro-tibial joint aredepicted at coincident functional positions as in FIGS. 28a-28e andwhere the extent of femoro-tibial contact area being indicated by theA-P contact length, as shown by empty triangles with the anterior aspectbeing to the left and posterior to the right;

FIGS. 30a-30e are sectional views of the total knee prosthesis shown inFIG. 15 through center Section C--C, where the articular mechanics ofhinge pin 115 within slotted hole 115d and of the central cam/followermechanism--consisting of the interior slightly concave surface portion129 of intercondylar housing 137 with the contacting exterior surfaces174a, 174b and 174c of upwardly extending tibial post 174--are depictedat identical functional positions as in FIGS. 28a-28e and 29a-29e andwhere the extent of central cam/follower bearing contact area beingindicated by the A-P contact length or traversing contact points, asshown by solid triangles with the anterior aspect being to the left andposterior to the right;

FIG. 31 is a medial side elevational view of a uni-axis design versionof the total knee prosthesis shown in FIG. 15 with numericaldesignations of similar portions being advanced by the number 100 andwith the left side of the drawing being the anterior aspect and thefrontal view being the medial aspect;

FIG. 32 is a rear (posterior) sectional view of the total kneeprosthesis shown in FIG. 31, showing the assembled position of hinge pin215 within the transverse ports 215b and 215a of posterior femoralcondyles 220 & 222 and within circular hole 215d in upwardly extendingtibial post 274 with the right side of the drawing being the lateralaspect of the uni-axis hinge prosthesis and the background directionbeing anterior;

FIGS. 33a-33c are lateral sectional views, through the indicated centralsectional plane of the total knee prosthesis shown in FIG. 31, where thearticular mechanics are depicted at the outset of flexion (FIG. 33a), atan intermediate position of 25 degrees flexion (FIG. 33b) and at maximumflexion of 140 degrees and with the extent of articular bearing contactof the inboard femoro-tibial joint being indicated by empty triangles,the extent of articular bearing contact of the outboard femoro-tibial(previously denoted as the cam/follower) bearing surfaces beingindicated by solid triangles and the extent of articular contact of theinterior surface 229 of intercondylar housing 237 and contacting bearingsurfaces 274a & 274c of upwardly extending tibial post 274 beingindicated by solid squares with the left side of the drawings being theanterior aspect and the right side being posterior.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The present invention pertains to a knee prosthesis which (a) can beutilized for primary resurfacing of the articular surfaces of the kneejoint, while retaining the posterior (and anterior) cruciate ligamentstructures--in the same manner as a number of currently availableconventional condylar resurfacing types of total knee prostheses and (b)can also be utilized to provide posterior stabilization, e.g.tibia-to-femur constraint, throughout the entire range of flexion andextension; thus, reducing the possibility of anterior subluxation ordislocation of the distal femur in clinical situations involvingincompetent, absent or purposely sacrificed posterior cruciate ligamentstructures or in the presence of inherent posterior tibial instability.

In this regard, therefore, the present prosthesis is categorized as acondylar resurfacing type of total knee prosthesis or a (totally)posterior stabilized total knee prosthesis device. This is accomplishedwithout the need of a conventional "stabilizer box" or other cumbersomemechanical gadgetry, which must be accommodated by substantial resectionof viable femur bone stock or which requires the complete sacrifice ofthe cruciate ligament structures for clearance purposes--even inclinical situations where viable ligament structures may exist at thetime of surgery.

Furthermore, in the present invention the posterior stabilizercam/follower members, are uniquely integrated within the outboardportion of the medial and lateral distal femoral condyles and respectiveoutboard portions of the UHMWPE tibial plateau bearing component and arespecially designed to provide both posterior stabilization and anatural-like femoro-tibial posterior rollback, commencing at the outsetflexion (at 0 degrees flexion or maximum hyperextension at about -6degrees flexion) and completing at approximately 30 degrees flexion.From 30 degrees flexion to full-flexion, both the cam/follower membermeans and the femoro-tibial member means attain a state of congruentcontact, which minimizes contact stress. Additionally, upon completionof the posterior rollback phase, the geometry of the contactingarticular bearing surfaces provides posterior (and anterior)stabilization of the knee joint; thus, reducing the possibility ofanterior (and posterior) subluxation or dislocation of the distal femur.

After the rollback phase, the outboard positioned posterior stabilizermembers function in concert with the inboard positioned medial andlateral femoro-tibial condylar bearing members to sustain, transfer anddistribute the imposed knee joint reaction forces to the underlyingcomponent fixation interfaces and adjacent supportive bone structure.The net effective articular bearing contact area, the summation of thatprovided by the cam/follower member means and by the femoro-tibialcondylar bearing member means, of the present invention is relativelysubstantial, increasing proportionally with flexion angle and attaininga maximum value at 55 degrees flexion equivalent to a 32 mm femoral(hip) head for intermediate sized knee components. From 55 degreesflexion to maximum flexion the net effective articular bearing contactarea is maintained at a constant value equal to the maximum level;therefore, tending to maintain a more acceptable and uniform level ofcontact stress within the functional range, usually associated withhigher levels of joint loading, than most other resurfacing or posteriorstabilizing types of total knee prosthesis designs.

Referring now to the Figure wherein like numerals designate like partsand particularly to FIG. 1, knee prosthesis 10 according to a firstembodiment of the present invention includes a femoral component 12 anda corresponding tibial component 14. Femoral component 12 incorporatesmulti-radius medial and lateral condylar runners or condyles 16 and 18,which mimic the natural femoral condyles of the distal femur that theyreplace. Specifically, medial and lateral femoral condyles 16 and 18include three distinct portions, that is, respective medial and lateralposterior condyle portions 20 and 22, distal femoral condyle portions 24and 26, and anterior femoral condyle portions 28 and 30.

It is a particular feature of the invention that the medial and lateraldistal femoral condyles 24 and 26 consist of inboard femoro-tibialdistal femoral condyles 24a and 26a and outboard medial and lateral cammembers 32. The medial and lateral cam members 32 consist of an anteriorconcave surface portion 32b and posterior convex cam member portion 32a.The medial and lateral posterior femoral condyles 20 and 22 consist ofmedial and lateral inboard portions 20a and 22a and medial and lateraloutboard portions 20b and 22b. The surface geometry of the inboardportions, 20a and 22a, and outboard portions 20b and 22b, of therespective posterior femoral condyles 20 and 22 is continuous and hasthe same radius of curvature R and center of curvature O (FIG. 5).

In addition, femoral component 12 includes medial and lateral cammembers 32, integrally positioned within the outboard portion of themedial and lateral distal femoral condyles 24 and 26, between theanterior femoral condyles 28 and 30 and posterior femoral condyles 20and 22 of medial and lateral femoral condyles 16 and 18, respectively.As shown in the first embodiment of FIGS. 1-12, cam members 32 areformed in two parts: the anterior concave surface portion 32b and theposterior convex portion 32a, each integral within the outboard portionof medial and lateral distal femoral condyles 24 and 26. Further, theradius of curvature R of the convex cam member 32a is identical to theradius of curvature R of the posterior portions 20 and 22 of the medialand lateral femoral condyles 16 and 18, the radius of curvature R of theoutboard (anterior to line 82) concave arcuate follower members 78, theradius of curvature R of the outboard posterior portion of tibialplateau bearing surfaces 62a and 64a and the radius of curvature R ofthe inboard posterior portion of the medial and lateral tibial plateaubearing surfaces 62 and 64, with the respective centers of curvaturelocated at points 0 and O', as shown in FIGS. 2, 5 and 14a.

The anterior portion of femoral component 12 is formed of theaforementioned anterior portions 26 and 30 of medial and lateralcondyles 16 and 18, and an anterior pateilar flange 36 integral with andinterconnecting anterior portions 28 and 30. The patella member 94(shown in phantom) articulates with the anterior patellar flange 36,biased laterally at the outset of flexion, and gradually transfersarticulation in a natural-like manner to the distal aspects of theanterior patellar flange 36 and the anterior condyle portions 28 and 30at approximately 25-30 degrees flexion. From this point on duringflexion and as the flexion angle increases to full range, thepatellar-femoral joint articulation progresses to the inside corners 38(FIGS. 4 and 7) of distal femoral condyle portions 24 and 26.

It is noted that the inside surfaces of femoral component 12 whichinterface directly with bone in the biological fixation mode or with aninterpositional thickness of polymethyl methacrylate (PMMA) bone cementin the cemented mode, are the inner anterior surface 40, the inneranterior-distal surface 42, the inner medial and lateral distal surfaces44 and 46, the inner medial and lateral distal-posterior surfaces 48 and50, and the inner medial and lateral posterior surfaces 52 and 54. Thesesurfaces may metallurgically incorporate an integral sintered, diffusionbonded or plasma sprayed porous surface structure 56, only a portion ofwhich is shown in FIGS. 4 and 6, as a component biological or cementedfixation means. In addition, upwardly extending cylindrical posts 55 maybe provided which fit into appropriately prepared holes in the distalend of the femur to aid in the translational and rotational fixationstability of the implanted femoral component.

In accordance with the invention, the maximum height of the cam members32, the follower members 76 and the central tibial eminence 74 do notextend beyond the thickness dimension of the distal femoral condyles 24and 26 and posterior femoral condyles 20 and 22 of medial and lateralfemoral condyles 16 and 18, at the level of the inside (bone-side)surface of inner distal surfaces 44 and 46, inner distal-posteriorsurfaces 48 and 50 and inner posterior surfaces 52 and 54. Additionally,the maximum width of the cam members 32, shown in FIG. 4 asapproximately half the overall distal condylar width, does not spatiallyobstruct the intercondylar space 37, as shown in FIGS. 6 and 7. As aconsequence of this design, the stabilizer box structure common to mostother posterior stabilizing total knee designs, is not required andaccommodation of the femoral component by resecting a significant"block" of viable bone from the intercondylar sector of the distal femuris unnecessary. In addition, as previously stated, the intercondylarspace 37 is spatially unobstructed, which can provide sufficientcontainment clearance for retained cruciate ligament structures, as asurgical alternative--even when current and long term viability statusof the structures cannot accurately be preoperatively orinteroperatively ascertained.

Further, the intercondylar opening 37 within the condyles 16 and 18 isformed by the posterior edge 29 of the anterior patellar flange 36 andthe medial and lateral edges 16a and 16b of the respective medial andlateral condyles 16 and 18. As previously stated, the boundaries ofopening 37 are essentially within the plane and maximum thickness of thedistal femoral condyles 24 and 26 and posterior femoral condyles 20 and22 of respective medial and lateral femoral condyles 16 and 18. However,an intercondylar stabilizer box, which generally (a) houses thecam/follower mechanism, (b) positionally invades the intercondylarspace, and (c) protrudes within the bone space of the distal femurrequiring absolute sacrifice of the posterior (and anterior) cruciateligaments and substantial removal of distal femoral bone to provide thenecessary clearance for component implantation, is not required by thepresent invention.

The UHMWPE tibial plateau bearing component 57 includes inboardequi-spaced concave multi-radius medial and lateral tibial plateaubearing surfaces 58 and 60, respectively, which receive convexmulti-radius medial and lateral femoral condyles 16 and 18, consistingof anterior condylar portions 28 and 30, inboard distal femoral condylarrunners 24a and 26a and inboard portions 20a and 22a of posteriorfemoral condyles 20 and 22, for articulation thereon. In like manner tocondyles 16 and 18, and because of the convex multi-radius shape oftibial plateau bearing surfaces 58 and 60, it will be appreciated thattibial plateau bearing surfaces 58 and 60 include anterior portions 70and 72, central portions 66 and 68, and posterior portions 62 and 64,respectively.

Between medial and lateral tibial plateau bearing surfaces 58 and 60,tibial plateau bearing component 57 includes an interconnecting,centrally positioned and anterior-posterior traversing tibial eminence74. During the early stages of flexion, the tibial eminence 74 ispositioned between the inside corners 38 and side walls 16a and 16b ofinboard distal portions 24a and 26a of medial and lateral femoralcondyles 16 and 18, respectively, as shown best in FIGS. 1 and 3,providing medial-lateral, axial and varus-valgus rotational kneeconstraint.

The degree of translational and rotational freedom exhibited byprostheses is a function of the dimensional clearance between theintercondylar space 37 of femoral component 12 between distal portions24a and 26a of medial and lateral condyles 16 and 18, and the mediallateral width of the tibial plateau bearing eminence 74. As the flexionangle increases, the inboard posterior femoral condyles 20a and 22a ofmedial and lateral condyles 16 and 18 span the posterior portion ofeminence 74. At the outset of flexion or maximum hyperextension, thedistal aspect of the anterior condylar portions 28 and 30 and theanterior aspect of the inboard medial and lateral distal femoralcondyles 24a and 26a of medial and lateral condyles 16 and 18,congruently contact the anterior portions 70 and 72 of inboard medialand lateral tibial plateau bearing surfaces 58 and 60, respectively; andthe concave surface portion 32b of medial and lateral cam member 32congruently contacts the convex portions 78a of medial and lateralfollower members 76, respectively--as best shown in FIG. 2--whichprovides both posterior (tibia-to-femur) and anterior (femur-to-tibia)stabilization of the hyperextended or 0 degree flexed knee joint.

In addition, tibial plateau bearing component 57 includes outboardmedial and lateral follower member means 76 consisting of respectiveanterior convex surface 78a, central concave arcuate follower membersurfaces 78, which extend anterior of mid-line 82 and outboard posteriorportion of the concave arcuate tibial plateau bearing surfaces 62a and64a, which extend posterior of mid-line 82. The medial and lateral cammembers 32 of femoral component 12 include a anterior concave surfaceportion 32b and a posterior convex portion 32a; after posterior rollbackis completed at approximately 30 degrees flexion the cam member functionis transferred to the outboard portion 20b and 22b of the medial andlateral posterior femoral condyles 20 and 22, respectively.

It will be appreciated that the concave arcuate follower members 78, theoutboard posterior portion of the tibial plateau bearing surfaces 62aand 64a and inboard posterior portion of the tibial plateau bearingsurfaces 62 and 64 are defined by the identical radius of curvature R,with the common center of curvature located at point O'. Similarly, theconvex cam member portion 32a of medial and lateral cam members 32 isalso defined by radius of curvature R centered at O' and the radius ofcurvature of the inboard portion, 20a and 22a, and the outboard portion,20b and 22b of the medial and lateral posterior femoral condyles 20 and22 is also equal to R; with the center of curvature located at pointO--as is best shown in FIGS. 2 and 5.

At the outset of knee flexion--corresponding to 6 degrees hyperextension(FIG. 13) or at 0 degrees flexion (FIG. 14a), depending upon selecteddesign criteria--the anterior concave cam member surface 32b andanterior convex follower surface 78a come into congruent contact and theanterior face of the convex cam members 32a of medial and lateral cammembers 32 congruently contacts the concave arcuate follower member 78,slightly anterior of the mid-line 82. This contact state between therespective cam members 32b and 32a and follower members 78a and 76represents the earliest stage of posterior (tibia-to-femur)stabilization, which occurs at the earliest stage of knee flexion.

As the flexion angle increases (FIG. 14b), the camming action betweenthe non-congruent contact of the anterior face of convex cam memberportions 32a of medial and lateral cam members 32 and the upward slopingconcave arcuate follower member portions 78 of medial and lateralfollower members 76, respectively, causes the center of curvature O ofthe medial and lateral posterior condyles 20 and 22 of femoral component12 to displace posteriorly and approach the center of curvature O' ofthe concave arcuate follower member portions 78, the outboard posteriorportion of the tibial plateau bearing surfaces 62a and 64a, and theinboard posterior portion of the tibial plateau bearing surfaces 62 and64. This allows the medial and lateral femoral condyles 16 and 18 offemoral component 12 to translate or roll back, posteriorly, relative tothe inboard medial and lateral tibial plateau bearing surfaces 58 and 60of tibial bearing component 57.

Posterior rollback of the femoro-tibial joint continues as the flexionangle increases and at 30 degrees flexion, shown in FIG. 14c, both thecenter of curvature O of posterior femoral condyles 20 and 22 and thecenter of curvature O' of the inboard and outboard posterior portions ofthe tibial plateau bearing surfaces 62 and 64, and 62a and 64a,respectively, coincide. When this occurs, the outboard portions 20b and22b of the medial and lateral posterior femoral condyles 20 and 22commence to function as cam member surfaces, and "link-up" and come intocongruent contact with the outboard posterior portion of the tibialplateau arcuate bearing surfaces 62a and 64a. Concurrently, the inboardportion of the medial and lateral posterior femoral condyles 20a and 22acome into congruent contact with the respective inboard posteriorportion of the tibial plateau bearing surfaces 62 and 64. At this pointin the flexion range (approximately 30 degrees flexion), the congruentarticular bearing contact area of the femoro-tibial joint (indicated asempty triangles in FIG. 14c ) and the congruent contact area of thecam/follower mechanism, e.g. the outboard portion 20b and 22b of theposterior femoral condyles 20 and 22 contacting the outboard posteriorportion of the tibial plateau bearing surfaces 62a and 64a (indicated assolid triangles in FIG. 14c), are equal in magnitude.

As the flexion angle increases (FIG. 14d) the articular bearing contactarea of the femoro-tibial joint (indicated as empty triangles) remainsconstant. The articular contact area of the cam/follower mechanismincreases proportionally with the flexion angle, since, the outboardportion 20b and 22b of the medial and lateral posterior femoral condyles20 and 22 contacts both the outboard posterior portion of the tibialplateau bearing surfaces 62a and 64a and also the concave arcuatefollower members 78 (indicated as solid triangles in FIG. 14d). Theresulting articular bearing contact area of the cam/follower mechanismincreases proportionally with the flexion angle to approximately 55degrees flexion, where maximum bearing area is attained. This maximumarticular contact area for knee components of intermediate size isequivalent to that of a 32 mm femoral (hip) head. From this point in theflexion range to maximum flexion the articular contact area of thecam/follower mechanism remains at a constant value--at the maximumlevel--as indicated as the solid triangles in FIG. 14d and 14e.

From approximately 30 degrees flexion to full flexion the radius ofcurvature R and center of curvature O of the inboard portions 20a and22a and outboard portions 20b and 22b of the medial and lateralposterior femoral condyles 20 and 22 are identical and coincident to theradius of curvature R and center of curvature O' of the outboardposterior portions of the tibial plateau bearing surfaces 62a and 64a,inboard posterior portions of the tibial plateau bearing surfaces 62 and64, and concave arcuate follower member surfaces 78. The resultingarticular bearing contact area of the cam/follower mechanism (indicatedas solid triangles in FIGS. 14c through 14e), therefore, compliments andaugments the articular contact area of the femoro-tibial joint(indicated as empty triangles in FIGS. 14c through 14e) fromapproximately 30 degrees flexion--where posterior rollback iscompleted--to full flexion. In this manner the cam/follower mechanism ofthe present invention (a.) provides posterior stabilization over theentire flexion range in surgical situations requiring either retentionor sacrifice of the posterior (and anterior) cruciate ligamentstructures; and (b.) can provide significant articular bearing surfacearea augmentation to the articular surfaces of the femoro-tibial jointto sustain, distribute and transfer the imposed knee joint reactionforces within the flexion range from approximately 30 degrees flexion tofull flexion.

Preferably and as shown in FIGS. 8a-8c, the tibial component 14 iscomprised of a UHMWPE tibial plateau bearing component or insert 57,which is assembled and interlocked onto the metallic alloy tibial basecomponent 84, via peripheral and centrally positioned engaging dovetailchannels 83a and 83, and securely wedged and locked into final seatedposition with locking screw 93 incorporating an external thread 87a,which is installed anteriorly through posteriorly inclined clearancehole 75 and engages threaded port 87 located at the locking wedgeportion 85 of tibial base component 84. The underside surface 86 oftibial base component 84 may incorporate a metallurgically integralsintered, diffusion bonded or plasma sprayed metallic alloy poroussurface structure 88 (shown in partial section in FIG. 12) as a cementedor as a biological ingrowth bone fixation means.

The tibial base component 84 may incorporate short integral pegstabilizers 90 and an intramedullary stem 91 for augmentation oftorsional and translational bone/prosthesis fixational constraint.Intramedullary stem 91 incorporates medial and lateral fixationstabilizing gussets 92 and a distal internal screw thread 88 (FIG. 2),which is oriented at posteriorly inclined angle 95 of approximately 3-5degrees to more appropriately comply with the physiological medullarycanal angulation of the tibial bone. The internal distal screw thread 88within the intramedullary stem 91 allows assembly via mating externalscrew thread 88a of plug component 89 or similarly, the assembly of anintermedullary stem extension (not shown) of up to 15 mm or morediameter and up to 300 mm or more in length, if additional componentstability is surgically indicated.

As still yet another principal embodiment of the present invention, therelatively large congruent bearing surface area of the cam/followerstabilizer mechanism and of the femoro-tibial joint, as described,advances the technical feasibility of employing ceramic-ceramic ormetal-metal or ceramic-metal articular bearing material couples in thedesign of knee prostheses to minimize potential effects of in-situgenerated wear surface particulates on bone morphology--recentlyassociated with the metal/UHMWPE articular material couple in both hipand knee joint prostheses. Therefore, it may now become more feasible tomanufacture the femoral component 12 and tibial plateau bearingcomponent 57 of more rigid and wear resistant bearing materials, anapproach which has not yet proven clinically feasible, relative toconventional knee prosthesis designs that generally employ "line"contact and associated high contact stress articular bearing geometry.

It will be appreciated that various changes or modifications can beincorporated into the present invention as claimed. For example, poroussurface 56 on bone apposition surfaces 40, 42, 44, 46, 48, 50, 52 and 54of femoral component 12 and porous surface 88 on bone apposition surface86 of the tibial base component 84 can be prepared with a hydroxyapatiteceramic coating for improved bone attachment fixation, or anintramedullary stem can be added to the femoral component 12 forimproved fixation stability, etc.

In accordance with a further aspect of the invention, prosthesis 10 maybe modified to facilitate rotation of the bones of the knee joint in twoplanes, and in particular, the rotation of the tibia in the plane of itslong axis. Generally, this capability is accomplished by themodification of the tibial component to cooperate with a flanged sleeveat the proximal insertion end thereof, which sleeve is fixed within thesurgically prepared tibial end. Such constructions and their variantsare shown in U.S. Pat. No. 4,136,405 to Pastrick et al. and U.S. Pat.No. 4,219,893 to Noiles, and the disclosures of these references areaccordingly incorporated herein by reference for such purpose. The exactconstruction of this rotation means may vary in accordance with theteachings of the referenced patents, so that the present tibialcomponent may be suitably modified in this fashion.

As stated earlier, the invention extends to the preparation of totalknee prostheses with the inclusion of a hinged attachment. Thisembodiment will be described in detail hereinbelow and with reference toFIGS. 15-33, wherein like parts have been given like number designationsadvanced by 100 or 200, as the case may be.

Referring now to FIGS. 15-33, a mechanically linked variable-axis totalknee prosthesis 110 according to this embodiment of the inventionincludes a metallic alloy femoral component 112, a corresponding tibialcomponent 114 and interconnecting hinge pin 115. Femoral component 112incorporates multi-radius medial and lateral condylar runners orcondyles 116 and 118, that essentially mimic the shape of the naturalfemoral condyles of the distal femur which they replace.

Specifically, medial and lateral femoral condyles 116 and 118 includethree distinct portions, that is, medial and lateral posterior condyleportions 120 and 122, respective distal femoral condyle portions 124 and126 and respective anterior femoral condyle portions 128 and 130. Themedial and lateral distal femoral condyles 124 and 126 compriserespective inboard distal femoral condyles 124a and 126a, and respectiveoutboard cam member means 132. Medial and lateral cam member means 132consist of anterior concave surface portion 132b and posterior convexcam member portion 132a. The medial and lateral posterior femoralcondyles 120 and 122 consist of medial and lateral inboard portions 120aand 122a, and medial and lateral outboard portions 120b and 122b,respectively. The surface geometry of inboard portions 120a and 122a andoutboard portions 120b and 122b of respective posterior femoral condyles120 and 122 are continuous and having the same radius of curvature R andcenter of curvature O (FIGS. 20 and 28a).

Medial and lateral posterior femoral condyles, or femoral hingecomponents 120 and 122 incorporate a hinge passageway or transversethrough port, 115b and 115a respectively, for insertion assembly of thehinge axis comprising hinge pin 115. An undercut locking groove 115c(FIG. 17) located concentrically within through port 115b in medialposterior femoral condyle 120 and positioned adjacent to the medial edgeaccepts locking ridge 195 for securing and locking of hinge pin 115therein. The center-axis location of medial transverse port 115b and oflateral transverse port 115a is coincident with center of curvature O ofthe medial and lateral femoral condyles 120 and 122. It is understoodthat the undercut locking groove 115c can also be incorporated withinlateral transverse port 115a of lateral posterior femoral condyle 122 orwithin both transverse ports, as well.

In addition, femoral component 112 includes medial and lateral cammember means 132, integrally positioned within the outboard portion ofthe medial and lateral distal femoral condyles 124 and 126, between therespective anterior femoral condyles 128 and 130 and posterior femoralcondyles 120 and 122 of medial and lateral femoral condyles 116 and 118.As shown in the first embodiment of FIGS. 15-27, medial and lateral cammember means 132 are formed in two parts; the anterior concave portion132b and the posterior convex cam surface portion 132a, each integraland continuous within the outboard portion of medial and lateral distalfemoral condyles 124 and 126. Further, the radius of curvature R ofmedial and lateral convex cam surface portions 132a is identical to theradius of curvature R of medial and lateral posterior femoral condyles120 and 122, the radius of curvature R of outboard (anterior to line182) medial and lateral concave arcuate follower member means 178, theradius of curvature R of outboard portion of medial and lateralposterior tibial plateau bearing surfaces 162a and 164a, and the radiusof curvature R of inboard portion of medial and lateral posterior tibialplateau bearing surfaces 162 and 164, with the respective centers ofcurvature located at points O and O', as shown in FIGS. 20, 23c and 28a.

The anterior portion of femoral component 112 is formed of theaforementioned anterior condyle portions 128 and 130 of medial andlateral condyles 116 and 118 and anterior patellar flange 136 integralwith and interconnecting anterior condyle portions 128 and 130. Thepatella member 194 (not shown) articulates with the anterior patellarflange 136, biased laterally, at the outset of flexion and graduallytransfers articulation in a natural-like manner to the distal aspects ofanterior patellar flange 136 and anterior condyles 128 and 130 atapproximately 25-30 degrees flexion.

The patella-femoral joint articulation then progresses to the insidecorners 138 (FIGS. 19 and 22) of inboard distal femoral condyle portions124a and 126a, traversing posteriorly, as the flexion angle increases tofull range. It is noted that the proximal fixation surfaces of femoralcomponent 112, which interface directly with bone in the biologicalfixation mode or with an interpositional thickness ofpolymethylmethacrylate (PMMA) bone cement in the cemented fixation mode,are the anterior surface 140, the medial and lateral anterior-distalsurfaces 142a and 142, the medial and lateral distal surfaces 144 and146, the medial and lateral distal-posterior surfaces 152 and 154 andalso medial and lateral side-walls 125 and 127 and exterior roof 131 ofintercondylar housing 137. These fixation surfaces may metallurgicallyincorporate an integral sintered, diffusion bonded or plasma sprayedporous surface structure 156, only a portion of which is shown in FIGS.15, 17, 18, 19 and 21, as a femoral component 112 biological or cementedfixation means. In addition upwardly extending (Morse) taperedintramedullary stem 139, integral with exterior roof 131 ofintercondylar housing 137, inserts into an appropriately prepared holewithin the axial centerline portion of the distal femur bone to provideadditional translational and varus-valgus rotational fixation stability.An intramedullary stem extension (not shown) can be added as a modularassembly, when additional component fixation is surgically indicated,and is attached and locked onto the Morse taper surface geometry ofintegral intramedullary stem 139.

Further, the centrally positioned intercondylar housing 137interconnects the lateral aspect of medial femoral condyle 116 and themedial aspect of lateral femorai condyle 118. Housing 137 is formedexternally by medial and lateral side-walls 125 and 127 and roof portion131 which function as fixation surfaces, and is formed internally bymedial and lateral intercondylar opening side-walls 116a and 116b andinterior roof portion 129 which function as articular bearingsurfaces--engaging exterior bearing surfaces 174a, 174b, 174c and 174dof upwardly extending tibial post 174 of tibial plateau bearingcomponent 157.

The tibial plateau bearing component 157 includes inboard concavemulti-radius medial and lateral tibial plateau bearing surfaces 158 and160 which receive the inboard portions of convex multi-radius medial andlateral femoral condyles 116 and 118 consisting of inboard distalportions of anterior femoral condyles 128 and 130, inboard distalfemoral condyles 124a and 126a and inboard portions 120a and 122a ofposterior femoral condyles 120 and 122 for articulation thereon. In likemanner it will be appreciated that the concave multi-radius shape of theinboard medial and lateral tibial plateau bearing surfaces 158 and 160include anterior portions 170 and 172, central portions 166 and 168 andposterior portions 162 and 164, respectively. Between inboard medial andlateral tibial plateau bearing surfaces 158 and 160, the tibial plateaubearing component 157 incorporates an interconnecting, centrallypositioned, anterior-posterior traversing and upwardly extending tibialpost 174. A slotted hole 115d within tibial post 174 (FIG. 23c), locatedat an identical center-axis level as medial and lateral transversethrough ports 115b and 115c within medial and lateral posterior condyles120 and 122, accepts hinge pin 115, thus constituting a (hinge axis)rotational and A-P translational bearing surface member and mechanicallinkage mechanism, interconnecting femoral component 112 and tibialcomponent 114. The diameter of slotted hole 115c is equal to thediameter of hinge pin 115, plus appropriate diametral clearance. Thelength of slotted hole 115c is defined anteriorly by center-axisposition O, the center of curvature of medial and lateral posteriorfemoral condyles 120 and 122 and of hinge pin 115; and posteriorly bycenter-axis position O', the center of curvature of medial and lateralconcave arcuate follower member portions 178, the center of curvature ofmedial and lateral outboard and inboard portions of posterior tibialplateau bearing surfaces 162a and 164a, and 162 and 164, respectively,and center of curvature of articular surface 174a of tibial post 174.

During the early stages of flexion, medial and lateral sidewall surfaces174d of tibial post 174 are positioned between respective inside corners138 and sidewall surfaces 116a and 116b of intercondylar housing 137,adjacent to respective inboard distal condyle portions 124a and 126a ofmedial and lateral femoral condyles 116 and 118, as shown best in FIGS.15, 17 and 18; providing semi-constrained medial-lateral andvarus-valgus rotational freedom. The extent of translational androtational freedom is a function of the dimensional clearances betweenthe opposing surfaces.

In addition at the outset of knee flexion, surface 174c of tibial post174 contacts the anterior aspect of interior roof 129 of intercondylarhousing 137, as best shown in FIG. 31a, and thereby functions as amechanical stop or constraint to hyperextension (return) motion of theknee joint, and also provides broad bearing contact area to complimentthe bearing contact surfaces of the inboard femoro-tibial joint andoutboard cam/follower members. Similarly, at the outset of flexion,medial and lateral anterior convex surface portions 178a of followermember means 176 contact respective concave surface portions 132b of cammember means 132, also functioning as a mechanical hyperextension stopand complimentary bearing contact surface. Also at this time, hinge pin115 is positioned within the anterior portion of slotted hole 115d oftibial post 174 at center-axis O, as shown in FIGS. 28aand 30a.

As the flexion angle increases beyond zero degrees, the articularinterface between the tibial post/intercondylar housing bearing surfacestraverses posteriorly along surface 129. The initial coupling takesplace with the anterior surface 174c, then with surface 174b and finallywith posterior surface 174a of tibial post 174, as shown in FIGS. 30athrough 30e. In the subsequent return or extension phase of knee motionthe exterior bearing surface portions 174a, 174b and 174c of tibial post174 with interior roof surface 129 of intercondylar housing 137 functionas a (centrally positioned) cam/follower mechanism, providing smoothretracement of femoro-tibial articular mechanics, as in the flexionphase.

At the outset of knee flexion, the distal aspect of the anterior femoralcondyles 128 and 130, and the anterior aspect of the inboard medial andlateral distal femoral condyles 124a and 126a of medial and lateralcondyles 116 and 118, congruently contact the anterior portions 170 and172 of inboard medial and lateral tibial plateau bearing surfaces 158and 160, respectively. Also at this time, the anterior concave surfaceportion 132b of medial and lateral cam members 132 congruently contactsthe anterior convex portion 178a of medial and lateral follower members176, respectively, as best shown in FIGS. 16 and 28a--with botharticular member surfaces providing both posterior (tibia-to-femur) andanterior (femur-to-tibia) stabilization of the extended or 0 degreeflexed knee joint.

Tibial plateau bearing component 157 includes outboard medial andlateral follower member means 176 consisting of respective anteriorconvex surface 178a, central concave arcuate follower member surfacemeans 178 extending anterior of mid-line 182, and outboard portion ofposterior concave arcuate tibial plateau bearing surfaces 162a and 164aextending posterior of mid-line 182. The medial and lateral cam membermeans 132 within respective distal femoral condyles 124 and 126 offemoral component 112 include an anterior concave surface portion 132band a posterior convex cam portion 132a. After posterior rollback iscompleted at approximately 25-30 degrees flexion to full flexion, thecam member function is transferred to the outboard portion 120b and 122bof the medial and lateral posterior femoral condyles 120 and 122,respectively. It will be appreciated that the medial and lateral concavearcuate follower member portion 178 of tibial plateau bearing component157, the respective outboard portions of the posterior tibial plateaubearing surfaces 162a and 164a and inboard portions of the posteriortibial plateau bearing surfaces 162 and 164 are defined by the identicalradius of curvature R with a common center of curvature located at pointO', as shown in FIG. 23c. It will be further appreciated that the convexcam member portion 132a of medial and lateral cam members 132 is alsodefined by radius of curvature R centered at O' as shown in FIG. 28a.Whereas, the radius of curvature R of medial and lateral inboardportions 120a and 122a and respective outboard portions 120b and 122b ofmedial and lateral posterior femoral condyles 120 and 122 is also equalto R, but with the center of curvature located at point O--as is bestshown in FIG. 20 and 28a.

Relative to the mechanics of the outboard cam/follower member means 132,at the outset of knee flexion the anterior concave cam member portion132b and anterior convex follower surface portion 178a come intocongruent contact and the anterior face of convex cam member portion132a of medial and lateral cam member means 132 congruently contacts theconcave arcuate follower member portion 178, anterior of the mid-line182, as shown best in FIGS. 28a and 29a. This contact state betweenmedial and lateral cam member portions 132b and 132a and respectivefollower member portions 178a and 178, represents the earliest stage ofposterior (tibia-to-femur) stabilization. As flexion angle increases(FIG. 28b), the camming action between the ensuing non-congruent contactof the convex cam member portions 132a of medial and lateral cam members132 and upward sloping concave arcuate follower member portions 178 ofmedial and lateral follower members 176, causes the center of curvatureO of the medial and lateral posterior condyles 120 and 122 of femoralcomponent 112 and of assembled hinge pin 115 to displace posteriorly,approaching center-axis O' of slotted hole 115c and coincident center ofcurvature O' of concave arcuate follower member portions 178, center ofcurvature O' of outboard portion of posterior tibial plateau bearingsurfaces 162a and 164a and center of curvature O' of inboard portion ofposterior tibial plateau bearing surfaces 162 and 164; therefore,allowing the inboard medial and lateral distal femoral condyles 124a and126 a of femoral component 112 to posteriorly translate or roll back,relative to the inboard medial and lateral tibial plateau bearingsurfaces 158 and 160 of tibial plateau bearing component 157.

Posterior rollback of the inboard femoro-tibial joint is concluded atapproximately 25-30 degrees flexion. As best shown in FIGS. 28c and 29c,both the center of curvature O of posterior femoral condyles 120 and 122and the center of curvature O' of the inboard and outboard portions ofposterior tibial plateau bearing surfaces (162 and 164) and (162a and164a), respectively, coincide. When this occurs, the outboard portions120b and 122b of medial and lateral posterior femoral condyles 120 and122 come into congruent contact with the outboard portion of posteriortibial plateau arcuate bearing surfaces 162a and 164a, as shown in FIG.28c.

Coincidentally, the inboard portions of the medial and lateral posteriorfemoral condyles 120a and 122a come into congruent contact with therespective inboard portion of posterior tibial plateau bearing surfaces162 and 164, as shown in FIG. 29c. At this point in the flexion range(approximately 25-30 degrees flexion), the extent of the resultingbearing contact area (contact length) of the femoro-tibial joint isindicated by the empty triangles in FIG. 29c and similarly, the extentof the resulting bearing contact area of the cam/follower mechanism,e.g. the outboard portion 120b and 122b of the posterior femoralcondyles 120 and 122 contacting the outboard portion of posterior tibialplateau bearing surfaces 162a and 164a is indicated by the solidtriangles in FIG. 28c.

As flexion angle increases from 25-30 degrees (FIG. 29c) to full flexion(FIG. 29e), the bearing contact area of the inboard femoro-tibial joint(indicated by the empty triangles) remains constant. The articularcontact area of the outboard medial and lateral cam/follower mechanisms,however, increases proportionally with flexion angles above the 25-30degree level (FIG. 28c), where the outboard portions 120b and 122b ofmedial and lateral posterior femoral condyles 120 and 122 maintaincontact congruency with the respective outboard portions of posteriortibial plateau bearing surfaces 162a and 164a, while subsequentlytraversing anteriorly, contacting the respective concave arcuatefollower members 178 in a proportional manner as the flexion angleincreases. The resulting bearing contact area of the outboard medial andlateral cam/follower mechanisms, therefore, increases proportionallywith the flexion angle from the 25-30 degree level (FIG. 28c) toapproximately 75 degrees flexion (FIG. 28d), where maximum bearingcontact area is attained. The magnitude of the resulting maximum contactarea for knee components of intermediate size is equivalent to that of a32 mm diameter (hip arthroplasty) femoral head. From this point in theflexion range to maximum flexion the bearing contact area of theoutboard medial and lateral cam/follower mechanisms is maintainedconstant at the maximum level, as indicated by the solid triangles inFIG. 28d and 28e.

After posterior femoro-tibial rollback at approximately 25-30 degreesflexion to full flexion, the radius of curvature R and center ofcurvature O of the inboard portions 120a and 122a and outboard portions120b and 122b of medial and lateral posterior femoral condyles 120 and122 are identical and coincident with the radius of curvature R andcenter of curvature O' of the outboard portions of respective posteriortibial plateau bearing surfaces 162a and 164a, of inboard portions ofrespective posterior tibial plateau bearing surfaces 162 and 164 and ofrespective outboard concave arcuate follower member surfaces 178, asshown in FIGS. 23c and 28c. The resulting bearing contact area of theoutboard medial and lateral cam/follower mechanisms (indicated by thesolid triangles in FIGS. 28a through 28e), the bearing contact area ofthe central cam/follower mechanism (indicated by the solid triangles inFIGS. 30a through 30e) and the mechanical linkage bearing of hinge pin115 within slotted hole 115d (FIGS. 30a through 30e), therefore bydesign, compliment and augment the bearing contact area of thefemoro-tibial joint (indicated by the empty triangles in FIGS. 29athrough 29e) to sustain, transfer and distribute the imposed knee jointreaction forces from the outset of knee flexion and throughout the fullflexion range.

Preferably, as shown in FIGS. 23a-23c, the tibial component 114 iscomprised of UHMWPE (ultra-high molecular weight polyethylene) tibialplateau bearing component 157, which is assembled and interlocked ontometallic alloy tibial base component 184 via side-posterior peripheraland central engaging dovetail channels 183a and 183, respectively. Inthis manner the tibial plateau bearing component 157 is securely wedgedand locked into final seated position by locking screw 193, which isinstalled anteriorly through anteriorly inclined clearance hole 175allowing screw thread 187a to engage threaded port 187, located withincentral wedge portion 185 of tibial base component 184. The undersidesurface 186 of tibial base component 184 may incorporate ametallurgically integral sintered, diffusion bonded or plasma sprayedmetallic alloy porous surface structure 188 (shown in partial section inFIG. 27) as a cemented or biological bone ingrowth fixation means. Thetibial base component 184 may incorporate short integral peg stabilizers190 and intramedullary stem 191 for improved prosthesis fixationalconsiderations. Intramedullary stem 191 incorporates medial and lateralfixation stabilizing gussets 192 and distal internal screw thread 188,which is oriented at an anteriorly inclined angle 194 of approximately3-5 degrees to more appropriately comply with the physiologicalmedullary canal orientation of the tibial bone. The internal distalscrew thread 188 within intramedullary stem 191 allows assembly, viamating external screw thread 188a, of stem plug component 189 orassembly of an intermedullary stem extension (not shown) of 15 mm ormore diameter and 300 mm or more in length, if additional tibialcomponent stability is surgically indicated.

As still yet another principal embodiment of the present invention, therelatively large congruent bearing contact surfaces of the outboardcam/follower mechanism, of the femoro-tibial joint and of the hingepin/tibial post connection, as described, increases the technicalfeasibility of employing ceramic-ceramic or metal-metal or ceramic-metalarticular bearing material couples to minimize potential adverse effectsof in-situ generated particulate wear debris on bonemorphology--recently associated with the metal/UHMWPE articular bearingcouple in both hip and knee joint prostheses. Therefore, it may nowbecome more feasible to manufacture the femoral component 112 and tibialplateau bearing component 157 of more rigid and more wear resistantbearing materials, an approach which has not yet proven clinicallyfeasible, relative to conventional knee prosthesis designs, whichgenerally employe "line" contact and associated high contact stressarticular bearing geometries.

It will be appreciated that various changes or modifications can beincorporated into the present invention as claimed. For example poroussurface 156 on fixation surfaces 140, 142, 142a, 144, 146, 152 and 154of femoral component 112 and porous surface 188 on fixation surface 186of the tibial base component 184 can be prepared with a hydroxyapatiteceramic coating for improved biological bone ingrowth fixation. Also,tibial bearing component 174 and engaging tibial base component 184 canbe designed according to known and clinically used methods (referenceU.S. Pat. No. 4,136,405 to Pastrick et al and U.S. Pat. No. 4,219,893 toNoiles), which employ a rotating platform to allow semi-constrained orunconstrained femoro-tibial axial rotational motion of the reconstructedknee joint.

The present variable-axis mechanically linked total knee prosthesisinvention can also be readily modified to reflect a more conventionaldesign, e.g. a uni-axis hinged-type total knee prosthesis, as shown inFIGS. 31 and 32. The numerical identification of similar constituentparts is consistent with FIGS. 15-27, however, is advanced by anumerical factor of 100.

The femoral component 212 of the uni-axis mechanically linked total kneeprosthesis 214 is essentially similar in design to femoral component 112of the variable-axis mechanically linked total knee prosthesis 114.Hinge pin 215 is identical to hinge pin 115 relative to location,functionality and method of retention within medial and lateral femoralcondyles 220 and 222; however, its relative femoro-tibial position isfixed throughout the flexion range. Upwardly extending tibial post 274remains centrally positioned and bounded between the lateral side 216bof medial femoral condyle 216 and the medial side 216a of lateralfemoral condyle 218 with exterior surfaces 274a, 274c and 274drespectively contacting interior roof surface 229 and surfaces 216a and216b of intercondylar housing 237.

The principal design difference of tibial post 274, compared to tibialpost 174, is the incorporation of a cylindrical transverse hinge pinhole 215c rather than the slotted hole 115c of the previous design;thus, functioning as a uni-axis bearing rather than a variable-axisbearing. The center axis of transverse hole 215c is coincident withcenter of curvature O of medial and lateral posterior femoral condyles220 and 222, center of curvature O of medial and lateral outboardconcave arcuate member portions 278 and center of curvature O ofoutboard and inboard portions of posterior tibial plateau bearingsurfaces (262a and 264a) and (262 and 264), as shown in FIG. 31; withrespective arcuate surface geometries defined by radius of curvature Rat center of curvature O. The outboard concave surface portions 232bwithin the anterior aspect of medial and lateral distal femoral condyles224 and 226, that contact respective convex surface portions 278a oftibial plateau bearing component 257, and anterior surface portion 274cof upwardly extending tibial post 274, that contacts anterior portion ofinterior roof 229 of intercondylar housing 237, function as mechanicalstops or constraints, thereby limiting the extent of hyperextension ofthe knee joint.

The principal embodiment of the present mechanically linked uni-axistotal knee prosthesis relates to the central intercondylar bearingmember surfaces, being comprised of anterior outer surface 274c andcentral-posterior outer surface 274a of upwardly extending tibial post274 articulating with interior roof surface 229 of intercondylar housing237 of femoral component 212. This articulation takes place throughoutthe flexion-extension range in a manner which compliments thefemoro-tibial joint bearing members being comprised of inboard portions220a and 222a of medial and lateral posterior femoral condyles 220 and222 articulating with respective inboard portions of posterior tibialplateau bearing surfaces 262 and 264 of tibial bearing component 257,and outboard portions 220b and 222b of medial and lateral posteriorcondyles 220 and 222 articulating with outboard portions of posteriortibial plateau bearing surfaces 262a and 264a and anterior arcuatesurface portions 278 of tibial plateau bearing component 257. Thisarticulation is best shown in FIGS. 33a-33c, which depicts a laterallydirected sagittal sectional view of the uni-axis mechanically linkedtotal knee prosthesis of FIG. 31 at the outset of flexion (FIG. 33a), at25 degrees flexion (FIG. 33b) and at full flexion (FIG. 33c). Thebearing contact length of the inboard femoro-tibial joint is indicatedby the empty triangles, the contact length of the outboard femoro-tibialjoint by the solid triangles and that of the central articularintercondylar surfaces by solid squares, which of course workconcurrently and in conjunction with the hinge pin/tibial post journalbearing surface to sustain, transfer and distribute the applied jointreaction forces of the functional knee joint.

Having described specific preferred embodiments of the present inventionwith reference to the accompanying drawings, it will be appreciated thatthe present invention is not limited to those precise embodiments, andthat various changes and modifications can be effected therein by one ofordinary skill in the art without departing from the spirit or scope ofthe invention as defined by the appended claims.

What is claimed is:
 1. A total knee prosthesis capable of providingresurfacing to adjacent ends of existing bone structures, as well astotal posterior stabilization to a knee joint, comprising:a) a femoralcomponent including:i) a medial condyle having an anterior portion, adistal portion and a posterior portion; ii) a lateral condyle having ananterior portion, a distal portion and a posterior portion; iii) ananterior patella flange interconnecting the anterior portions of themedial and lateral condyles in parallel, spaced apart relation; and iv)cam member means integral with said medial and lateral condyles andlocated outboard thereof, said cam member means having an anteriorlylocated concave cam member surface and a posteriorly located convex cammember surface; b) a tibial component including:i) multi-radius tibiasplateau bearing surface means for receiving said medial and lateralcondyles for rolling and sliding movement thereon; and ii) followermember means integral with said bearing surface means for receiving thecam member surfaces of said cam member means for rotational and slidingmovement thereon; and c) the cam member surfaces of said cam membermeans being in contact with said follower member means for substantiallythe entire flexion range of the knee,wherein said tibial plateau bearingsurface means includes: a. a medial multi-radius tibial plateau bearingsurface means located inboard of said follower means and having ananterior, central and posterior portion for receiving said medialfemoral condyle for rolling and sliding movement thereon; b. a lateralinboard multi-radius tibial plateau bearing surface means locatedinboard of said follower means and having an anterior, central andposterior portion for receiving said inboard portion of the lateralfemoral condyle for rolling and sliding movement thereon; c. a medialoutboard-located follower member consisting of a convex follower membersurface anteriorly and a concave arcuate follower member surfaceposteriorly for receiving said anterior concave cam member surface andposterior convex cam member surface of the medial cam member means forrolling and sliding movement thereon, said medial concave arcuatefollower member surface being connected to the respective posteriorportion of the concave arcuate tibial plateau bearing surface means; d.a lateral outboard-located follower member consisting of a convexfollower member surface anteriorly and a concave arcuate follower membersurface posteriorly for receiving said anterior concave cam membersurface and posterior convex cam member surface of the medial cam membermeans for rolling and sliding movement thereon, said lateral concavearcuate follower member surface being connected to the respectiveposterior portion of the concave arcuate tibial plateau bearing surfacemeans; and e. an interconnecting intercondylar eminence centrallydisposed between the medial and lateral multi-radius tibial plateaubearing surface means, said interconnecting eminence being connected tosaid plateau bearing surface means, and said being removed within theposterior intercondylar portion to provide required clearance forretained anterior and posterior cruciate ligament structures.
 2. A totalknee prosthesis according to claim 1, wherein said convex cam memberintegrated within the outboard portion of the medial and lateral distalfemoral condyles has a center of curvature being substantially the sameas a center of curvature of said respective outboard concave arcuatefollower members, of said respective outboard posterior portion of theconcave arcuate tibial plateau bearing surface means and of saidrespective inboard posterior portion of the concave arcuatefemoro-tibial plateau bearing surface members means.
 3. A total kneeprosthesis according to claim 1, wherein said medial and lateralposterior femoral condyles have a radius of curvature substantially thesame as a radius of curvature of said respective outboard convex cammembers, of said respective outboard concave arcuate follower members,of said respective outboard posterior portion of the concave arcuatetibial plateau bearing surface means, and of said respective inboardposterior portions of the concave arcuate femoro-tibial plateau bearingsurface member means.
 4. A total knee prosthesis according to claim 1,wherein said medial and lateral posterior femoral condyles have a centerof curvature that is displaced anteriorly by some small distancerelative to a center of curvature of said medial and lateral outboardconvex cam member means, of said respective outboard concave arcuatefollower member means, of said respective outboard posterior portion ofthe concave arcuate tibial plateau bearing surface means and of saidrespective inboard posterior portions of the concave arcuatefemoro-tibial plateau bearing surface member means.
 5. A total kneeprosthesis according to claim 1, wherein said tibial component includesa tibial plateau bearing component containing medial and lateralmulti-radius femoro-tibial plateau bearing surface means, aninterconnecting centrally disposed eminence and outboard-located medialand lateral follower member means, and a tibial base component connectedto an underside of said tibial plateau bearing component by means of acontinuous and wedging peripheral and central engaging dovetailstructures and preloaded and secured with a screw thread locking meanswhich is installed anteriorly.
 6. A total knee prosthesis capable ofproviding resurfacing to adjacent ends of existing bone structures, aswell as to a posterior stabilization to a knee joint, comprising:a) afemoral component including:i) a medial condyle having an anteriorportion, a distal portion and a posterior portion; ii) a lateral condylehaving an anterior portion, a distal portion and a posterior portion;iii) an anterior patella flange interconnecting the anterior portions ofthe medial and lateral condyles in parallel, spaced apart relation; andiv) cam member means integral with said medial and lateral condyles andlocated outboard thereof, said cam member means having an anteriorlylocated concave cam member surface and a posteriorly located convex cammember surface; b) a tibial component including:i) multi-radius tibialplateau bearing surface means for receiving said medial and lateralcondyles for rolling and sliding movement thereon; and ii) followermember means integral with said bearing surfaces for receiving the camsurfaces of said cam member means for rotational and sliding movementthereon; and c) said convex cam member surface being in sliding contactwith said follower member means to provide posterior rollback of saidcondyles on said tibial plateau bearing surface means during flexion,starting at approximately maximum normal hyperextension of flexion, andbeing completed at an angle less than approximately 40° offlexion,wherein said tibial plateau bearing surface means includes: a. amedial multi-radius tibial plateau bearing surface means located inboardof said follower means and having an anterior, central and posteriorportion for receiving said medial femoral condyle for rolling andsliding movement thereon; b. a lateral inboard multi-radius tibialplateau bearing surface means located inboard of said follower means andhaving an anterior, central and posterior portion for receiving saidinboard portion of the lateral femoral condyle for rolling and slidingmovement thereon; c. a medial outboard-located follower memberconsisting of a convex follower member surface anteriorly and a concavearcuate follower member surface posteriorly for receiving said anteriorconcave cam member surface and posterior convex cam member surface ofthe medial cam member means for rolling and sliding movement thereon,said medial concave arcuate follower member surface being connected to arespective posterior portion of the concave arcuate tibial plateaubearing surface means; d. a lateral outboard-located follower memberconsisting of a convex follower member surface anteriorly and a concavearcuate follower member surface posteriorly for receiving said anteriorconcave cam member surface and posterior convex cam member surface ofthe medial cam member means for rolling and sliding movement thereon,said lateral concave arcuate follower member surface being connected tothe respective posterior portion of the concave arcuate tibial plateaubearing surface means; and e. an interconnecting intercondylar eminencecentrally disposed between the medial and lateral multi-radius tibialplateau bearing surface means, said interconnecting eminence beingconnected to said plateau bearing surface means, and said eminence beingremoved within a posterior intercondylar portion to provide requiredclearance for retained anterior and posterior cruciate ligamentstructures.
 7. A total knee prosthesis according to claim 6, whereinsaid convex cam member integrated within the outboard portion of themedial and lateral distal femoral condyles has a center of curvaturebeing substantially the same as the center of curvature of saidrespective outboard concave arcuate follower members, of said respectiveoutboard posterior portion of the concave arcuate tibial plateau bearingsurface member means and of said respective inboard posterior portion ofthe concave arcuate femoro-tibial plateau bearing surface members means.8. A total knee prosthesis according to claim 6, wherein said medial andlateral posterior femoral condyles have a radius of curvaturesubstantially the same as the radius of curvature of said respectiveoutboard convex cam members, of said respective outboard concave arcuatefollower members, of said respective outboard posterior portion of theconcave arcuate tibial plateau bearing surface means, and of saidrespective inboard posterior portions of the concave arcuatefemoro-tibial plateau bearing surface member means.
 9. A total kneeprosthesis according to claim 6, wherein said medial and lateralposterior femoral condyles have a center of curvature that is displacedanteriorly by some small distance relative to a center of curvature ofsaid medial and lateral outboard convex cam member means, of saidrespective outboard concave arcuate follower member means, of saidrespective outboard posterior portion of the concave arcuate tibialplateau bearing surface means and of said respective inboard posteriorportions of the concave arcuate femoro-tibial plateau bearing surfacemember means.
 10. A total knee prosthesis capable of providingresurfacing to adjacent ends of existing bone structures, as well astotal posterior stabilization to a knee joint, comprising:a) a femoralcomponent including:i) a medial condyle having an anterior portion, adistal portion and a posterior portion; ii) a lateral condyle having ananterior portion, a distal portion and a posterior portion; iii) ananterior patella flange interconnecting the anterior portions of themedial and lateral condyles in parallel, spaced apart relation; and iv)cam member means integral with said medial and lateral condyles andlocated outboard thereof, said cam member means having an anteriorlylocated concave cam member surface and a posteriorly located convex cammember surface; b) a tibial component including:i) multi-radius tibialplateau bearing surface means for receiving said medial and lateralcondyles for rolling and sliding movement thereon; and ii) followermember means integral with said bearing surfaces for receiving the camsurfaces of said cam member means for rotational and sliding movementthereon; and c) said convex cam member surface being in sliding contactwith said follower member means to provide posterior rollback of saidcondyles on said tibial plateau bearing surface means during flexion,starting at approximately maximum normal hyperextension of flexion, andbeing completed at an angle less than approximately 40° offlexion,wherein said tibial component includes a tibial plateau bearingcomponent containing medial and lateral multi-radius femoro-tibialplateau bearing surface means, an interconnecting centrally disposedeminence and outboard-located medial and lateral follower member means,and a tibial base component connected to an underside of said tibialplateau bearing component by means of a continuous and wedgingperipheral and central engaging dovetail structures and preloaded andsecured with a screw thread locking means which is installed anteriorly.11. A total knee prosthesis capable of providing resurfacing to adjacentends of existing bone structures, as well as total posteriorstabilization to a knee joint, comprising:a) a femoral componentincluding:i) a medial condyle having an anterior portion, a distalportion and a posterior portion; ii) a lateral condyle having ananterior portion, a distal portion and a posterior portion; iii) ananterior patella flange interconnecting the anterior portions of themedial and lateral condyles in parallel, spaced apart relation; and iv)a cam member means integral with said medial and lateral condyles andlocated outboard thereof, said cam member means having an anteriorlylocated concave cam member surface and a posteriorly located convex cammember surface; b) a tibial component including:i) multi-radius tibialplateau bearing surface means for receiving said medial and lateralcondyles for rolling and sliding movement thereon; and ii) followermember means integral with said bearing surfaces for receiving the cammember surfaces of said cam member means for rotational and slidingmovement thereon; and c) said convex cam surface being in congruentcontact with said follower member means from approximately the end ofposterior rollback to full flexion,wherein said tibial plateau bearingsurface means includes: a. a medial multi-radius tibial plateau bearingsurface means located inboard of said follower means and having ananterior, central and posterior portion for receiving said medialfemoral condyle for rolling and sliding movement thereon; b. a lateralinboard multi-radius tibial plateau bearing surface means locatedinboard of said follower means and having an anterior, central andposterior portion for receiving said inboard portion of the lateralfemoral condyle for rolling and sliding movement thereon; c. a medialoutboard-located follower member consisting of a convex follower membersurface anteriorly and a concave arcuate follower member surfaceposteriorly for receiving said anterior concave cam member surface andposterior convex cam member surface of the medial cam member means forrolling and sliding movement thereon, said medial concave arcuatefollower member surface being connected to the respective posteriorportion of the concave arcuate tibial plateau bearing surface means; d.a lateral outboard-located follower member consisting of a convexfollower member surface anteriorly and a concave arcuate follower membersurface posteriorly for receiving said anterior concave cam membersurface and posterior convex cam member surface of the medial cam membermeans for rolling and sliding movement thereon, said lateral concavearcuate follower member surface being connected to the respectiveposterior portion of the concave arcuate tibial plateau bearing surfacemeans; and e. an interconnecting intercondylar eminence centrallydisposed between the medial and lateral multi-radius tibial plateaubearing surface means, said interconnecting eminence being connected tosaid plateau bearing surface means, and said eminence being removedwithin a posterior intercondylar portion to provide required clearancefor retained anterior and posterior cruciate ligament structures.
 12. Atotal knee prosthesis according to claim 11, wherein said convex cammember integrated within the outboard portion of the medial and lateraldistal femoral condyles has a center of curvature being substantiallythe same as a center of curvature of said respective outboard concavearcuate follower members, of said respective outboard posterior portionof the concave arcuate tibial plateau bearing surface member means andof said respective inboard posterior portion of the concave arcuatefemoro-tibial plateau bearing surface members means.
 13. A total kneeprosthesis according to claim 11, wherein said medial and lateralposterior femoral condyles have a radius of curvature substantially thesame as a radius of curvature of said respective outboard convex cammembers, of said respective outboard concave arcuate follower members,of said respective outboard posterior portion of the concave arcuatetibial plateau bearing surface means, and of said respective inboardposterior portions of the concave arcuate femoro-tibial plateau bearingsurface member means.
 14. A total knee prosthesis according to claim 11,wherein said medial and lateral posterior femoral condyles have a centerof curvature that is displaced anteriorly by some small distancerelative to a center of curvature of said medial and lateral outboardconvex cam member means, of said respective outboard concave arcuatefollower member means, of said respective outboard posterior portion ofthe concave arcuate tibial plateau bearing surface means and of saidrespective inboard posterior portions of the concave arcuatefemoro-tibial plateau bearing surface member means.
 15. A total kneeprosthesis capable of providing resurfacing to adjacent ends of existingbone structures, as well as total posterior stabilization to a kneejoint, comprising:a) a femoral component including:i) a medial condylehaving an anterior portion, a distal portion and a posterior portion;ii) a lateral condyle having an anterior portion, a distal portion and aposterior portion; iii) an anterior patella flange interconnecting theanterior portions of the medial and lateral condyles in parallel, spacedapart relation; and iv) a cam member means integral with said medial andlateral condyles and located outboard thereof, said cam member meanshaving an anteriorly located concave cam member surface and aposteriorly located convex cam member surface; b) a tibial componentincluding:i) multi-radius tibial plateau bearing surface means forreceiving said medial and lateral condyles for rolling and slidingmovement thereon; and ii) follower member means integral with saidbearing surfaces for receiving the cam member surfaces of said cammember means for rotational and sliding movement thereon; and c) saidconvex cam surface being in congruent contact with said follower membermeans from approximately the end of posterior rollback to fullflexion,wherein said tibial component includes a tibial plateau bearingcomponent containing medial and lateral multi-radius femoro-tibialplateau bearing surface means, an interconnecting centrally disposedeminence and outboard-located medial and lateral follower member means,and a tibial base component connected to an underside of said tibialplateau bearing component by means of a continuous and wedgingperipheral and central engaging dovetail structures and preloaded andsecured with a screw thread locking means which is installed anteriorly.16. A total knee prosthesis capable of providing resurfacing to adjacentends of existing bone structures, as well as total posteriorstabilization to a knee joint, comprising:a. a femoral componentincluding:i. a medial condyle having an anterior condyle portion, aninboard (lateral) distal condyle portion with outboard (medial) cammember means and a posterior condyle portion; ii. a lateral condylehaving an anterior portion, an inboard (medial) distal condyle portionwith outboard (lateral) cam member means and a posterior condyleportion; iii. an anterior patella flange interconnecting the anteriorportions of the medial and lateral condyles in parallel, spaced apartrelation; and iv. a cam member means integrated within the outboardportion of the medial and lateral condyles, said cam members having aconcave surface portion anteriorly and a convex cam member surfaceposteriorly; b. a tibial component including:i. a medial inboardmulti-radius tibial plateau bearing surface means having an anterior,central and posterior portion for receiving said inboard portion of themulti-radius medial femoral condyle for rolling and sliding movementthereon; and ii. a lateral inboard multi-radius tibial plateau bearingsurface means having an anterior, central and posterior portion forreceiving said inboard portion of the multi-radius lateral femoralcondyle for rolling and sliding movement thereon; and iii. a medialoutboard follower member comprising a convex surface anteriorly and aconcave arcuate follower member surface posteriorly for receiving saidanterior concave cam surface and posterior convex cam member surface ofmedial cam member means for rotational and sliding movement thereon,said medial outboard concave arcuate follower member surface means beingconnected with the respective outboard posterior portion of said inboardand outboard concave arcuate tibial plateau bearing surface means; andiv. a lateral outboard follower member consisting of a convex surfaceanteriorly and a concave arcuate follower member surface posteriorly forreceiving said anterior concave cam surface and posterior convex cammember surface of lateral cam member means for rotational and slidingmovement thereon, said lateral outboard concave arcuate follower membersurface means being connected with the respective outboard posteriorportion of the concave arcuate tibial plateau bearing surface means; andv. an interconnecting intercondylar eminence centrally disposed betweenthe medial and lateral inboard multi-radius tibial plateau bearingsurface means with said interconnecting eminence being connected to saidinboard plateau bearing surface means and said eminence being removedwithin a posterior intercondylar portion to provide required clearancefor retained anterior and posterior cruciate ligament structures; c.said medial and lateral cam member means being in contact with saidrespective follower member means from the outset of flexion and saidmedial and lateral cam member means being in contact with saidrespective follower member means substantially throughout the entireflexion range of the knee joint, providing uninterrupted posterior(tibia-femur) stabilization.